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SCIENTIFIC WRITINGS 



JOSEPH HENEY. 



VOLUME II. 




WASTITNGTON: 

PUBLISIIKD liy THK SMITilSONTAN INSTITUTION. 

1886. 



-2 3 ^/S, 




Stereotyped and Printed 
By JUDD (& DETWEILER, 

WAaHINOTOM, D. C. 



LIST OF ILLUSTRATIONS IN VOLUME II. 



Paob. 
Polar projection of Earth's northern hemisphere .62 

Isothermal map of the United States . .72 

Wind-roses : (New York, and New England) . .77 

Do. (Illinois, Wisconsin, Iowa, Pennsylvania) . 78 

Do. (Oregon, Washington, Nohnu»ka, Kansas) . . 79 

Do. (Texas, New Mexico, S. Carolina, Georgia, Ala., Miss.) 79 

Do. (Lower California) . . . . .80 

Do. (Hudson, Albany, Utica, N. Y.) .80 

Dalton's instrument for testing elastic force of aqueous vapor 216 

Instrument for showing varying elastic force of aqueous vapor 219 

Instrument for determining the weight of vapor . . 222, 228 

Water bulb used in the same ...... 223 

Ideal section, showing aerial cin^ulation of the northern hemi^^phe^e . 275 
Surface winds of the globe ...... 276 

Ideal section across the equator at the belt of calms . 277 

Diagram showing strata of expanding atmosphere . . 278 

Ocean currents of the western heiiiisphcre . . . 284 

Wind and timber map of the United States .... 288 

Motions of the air producing thundor-stonns . . . 296 

Motions of strata of the atino.<?phore in larger storms . . 303 

Production of electricity by means of glass slip and woolen cloth 315 

Electroscope, with gold-leaf strips, or suspended pith balls . 317 

Insulated hollow metallic globe, olectrified at surface only . 322 

Insulated cylinder of wire gauze, showing same . . 323 

Diagram showing resultant of exterior attraction or repulsion 324 

Diagram showing resultant of interior attraction or repulsion 325 

Diagram illustrating repulsion through projecting rod or wire . 325 

Illustration of electrical induction ..... 828 

Induction from electrical spark, through two stories of a house . 333 

Induction from distant lightning, shown in study window . 334 

(V) 



VI 



LIST OF ILLUSTRATIONS. 



Page. 

lUustmtion of surface tension of electricity .... 342 

Saussuro's elcctroscopic explorer ... 351 

Use of iSuii.s8iire'.s elcctroscopic explorer (2 tli^.) 352 

Induction from the earth shown by insuliited vertical r^xl . 352 

Dellnian's apparatus for oxhibitinij^ atmospheric electricity . . 354 

Peltier's electromotor ....... 355 

Changed sign of induced electricity at different heights 856 

Hour-glass appearance of thunder-cloud .... 3G0 

m 

Illustration of remarkable induction effect from distant lightning . 309 

Oersted's deflection of magnetic needle by galvanic current . 427 

Magnetization of iron-filings by galvanic current 427 

Arrago's method of magnetizing sewing-needles, &c. 428 
Sturgeon's first horse-shoe electro-magnet . . . .420 

Improvement of the horse-shoe magnet (First " intensity " magnet) . 420 

Magnet of compound helices (Improved "quantity " mognet) 430 

Electro-magnotic bell signal at Albany in 1831 434 



CONTENTS. 



Volume II. 



PART II— CONTINUED. 

Meteorology: Notes on rain-gages 

Meteorology : On the rain-full at difTerent heights 

Meteorology in its connection with Agriculture 

Part I. General considerations 

Part II. Genenil atmospheric conditions 

Part III. Terrestial physics, and tempomture . 

Part IV. Atmospheric vapor and currents-^ . 

Part V. Atmospheric electricity ^ 

On Acoustics applied to public buildings 

Account of a* large sulphuric-acid barometer in the Smith 
sonian Institution ..... 

Statement in relation to the history of the electro-magnetic 
telegniph ...... 

On the application of the telegraph to the premonition of 
weather-changes ..... 

On the utilization of aerial currents in Aeronautics . 

Systematic meteorology in the United States . 

Remarks on " Vitality " .... 

Suggestions as to the establishment of a Physical Observatory 

Effect of the Moon on the weather 

On the organization of a scientific society. [An address.] 

On the employment of mineral oil for light-house illumination 

Investigations relative to illuminating materials 

On the organization of local scientific societies 

The method of scientific investigation, and its applicati(»n to 
some abnormal phenomena of sound. [An address.] 

Observations in regard to thunder-storms 

Opening address to the National Academy of Sciences 

Closing address to the National Academy of Sciences 



Tkab. 
(1855] 
(1856] 
(1855] 

(185C; 
(1857] 
(1858; 
(1859] 
(1856; 

(1856] 

(1857; 

(1859] 

(1861; 

(1865] 

(1806] 

(1870) 

(187i; 

(1871 

(1875] 

(1875] 

(1875] 

(1877; 
(1878] 
(1878; 
(1878] 

(iii) 



Paob. 
1 

4 

6 

6 

33 

85 

212 

309 

403 

421 

426 

438 
443 
446 
457 
461 
466 
468 
476 
477 
511 

514 
529 
536 
538 



SCIENTIFIC WRITINGS 



JOSEPH HENEY. 



TOLUME II. 




"WASiriNGTON; 
PUBLISUED JiY TUK SMITUSONIAN INSTITUTION. 



2 WRITINGS OP JOSEPH HENRY. [1855 

the funnel. To prevent the rain-drops which may fall on 
this board from spattering into the mouth of the funnel 
some pieces of old cloth or carpet may be tacked upon it. 

The object of placing the receiving ring so near the sur- 
face of the earth is to avoid eddies caused by the wind, which 
might disturb the uniformity of the fall of rain. 

In the morning, or after a shower of rain, the bottle is 
taken up and its contents measured in the graduated tube 
belonging to the apparatus, and the quantity in inches and 
parts recorded in the register. The tube or gage which was 
first provided for this purpose will contain when full only 
one-tenth of an inch of rain, the divisions indicating hun- 
dredths and thousandths of an inch. As this however is 
found to be too small for convenience, another gage — which 
will contain an inch of rain, and indicating tenths and hun- 
dredths — will be sent to observers. 

Another and simpler form of the gage has since been 
adopted by the Institution and Patent OflBce, to send by 
mail to distant observers. It is one of those which have 
been experimented on at the Institution, and is a modifica- 
tion of a gage received from Scotland, which was recom- 
mended by Mr. Robert Russell. 

It consists of — I. A large brass cylinder, two inches in 
diameter, to catch the rain: 2. A smaller but longer brass 
cylinder for receiving the water and reducing the diameter 
of the column, to allow of greater accuracy in measuring 
the height : 3. A whalebone scale divided by experiment, so 
as to indicate tenths and hundredths of an inch of rain: 4. 
A wooden cylinder to be inserted permanently in the ground 
for the protection and ready adjustment of the instrument. 
To facilitate the transportation, the larger and smaller cylin- 
ders are connected together by a screw-joint. 

To put up this rain-gage for use — 1. Let the wooden cylin- 
der be sunk into the ground, in a level unsheltered place, 
until its upper end is even with the surface of the earth : 2. 
Screw the larger brass cylinder on the top of the brass tube 
and place the latter into the hole in the axis of the wooden 
cylinder, and the arrangement is completed. 



1855] WRITINGS OP JOSEPH HENRY. 3 

The depth of rain is measured by means of the whalebone 
scale, the superficial grease of which should be removed by 
rubbing it with a moist cloth before its use. Should the 
fall of rain be more than sufficient to fill the smaller tube 
then the excess must be poured out into another vessel, and 
the whole measured in the small tube in portions. 

Care should be taken to place the rain-gage in a level field 
or open space sufficiently removed from all objects which 
would prevent the free access of rain, even when it is falling 
at the most oblique angle during a strong w^nd. A con- 
siderable space also around the mouthof the funnel should 
be kept free from plants— as weeds or long grass, and the 
ground should be so level as to prevent the formation of 
eddies or variations in the velocity of the wind. 

Meamring snow. — To ascertain the amount of water pro- 
duced from snow, a column of the depth of the fall of snow 
and of the same diameter as the mouth of the funnel should 
be melted and measured as so much rain. The simplest 
method of obtaining a column of snow for this purpose is to 
procure a tin tube about two feet long (having one end closed) 
and precisely of the diameter of the mouth of the gage. 
With the open end downward, press this tube perpendicu- 
larly into the snow until it reaches the ground, or the top 
of the ice, or last preceding snow; then take a plate of tin 
sufficiently large to cover it, pass it between the mouth of 
the tube and the ground, and invert the tube. The snow 
contained in the tube, when melted, may be measured as so 
much rain. When the snow is adhesive, the use of the tin 
plate will not be necessary. 

From measurements of this kind/repeated in several places 
when the depth of the snow is unequal, an average quantity 
may be obtained. As a general average, it will be found 
that about ten inches of snow will make one inch of water. 



WRITINGS OP JOSEPH HENRY. [IMS 



ON THE RAIN-FALL AT DIFFERENT HEIGHTS. 
(From tho Smithsonian Annual Report for 1856, pp. 218| 214.)* 

December^ 1855. 

The subject of the difference of rain at different elevations 
has received much attention in this country and in Europe; 
though more investigations are required to settle definitely 
all the principles on which it depends. It would appear 
that the greater part of the observed difference is due to 
eddies of wind, which carry the air containing the falling ' 
drops more rapidly over the mouth of the upper gauge 
than over an equal portion of the unobstructed surface 
of the ground. Professor Bache found, from a series of 
observations on tho top and at the bottom of a shot-tower in 
Philadelphia, that not only was there a difference due to 
elevation, but also to the position of the upper gauge, whether 
it was placed on the windward or leeward side of the tower. 
It would also appear, that when the air is saturated with 
moisture down to the surface of the earth, the descending 
drop would collect at least a portion of the water it meets 
with in its passage to the ground, but the amount thus col- 
lected would not be sufficient to account for the difference 
observed. Besides this, the condition does not always exist; 
the air near the earth is frequently under-saturated during 
rain, and in this case a portion of the drop would be evapo- 
rated, and its size on reaching the earth loss than it was 
above. If the drop is increased by the deposition of new 
vapor in its descent, then the rain at the bottom ought to 
be warmer than at the top, on account of the latent heat 
evolved in the condensation; on the other hand, if the drop 
be diminished by evaporization during its fall, then the tem- 
perature of the rain caught at the greater elevation ought to 
be in excess. That evaporization does sometimes take place 
during the fall of rain, would appear from the fact that 

* [Remarks appended to an article on tho subject, by Prof. 0. W. Morris, 
of New York.] 



1855] WRITINGS OF JOSEPH HENRY. 5 

clouds are seen to exhibit the appearance of giving out rain 
though none falls to the earth, the whole being entirely 
evaporated. That the air should ever be under-saturated 
during rain is at first sight a very surprising fact; it may 
however be accounted for on the principle of capillarity. 
The attraction of the surface of a spherical portion of water 
for itself is in proportion to the curvature or the sinallness 
of the quantity, and hence the tendency to evaporate in a 
rain-drop ought to be much less than in an equal portion of 
a flat surface of water. 

If the diminution of quantity of rain at the upper station 
depends principally on eddies of wind, then the effect will 
be diminished by an increase in the size of the drops, which 
will give them a greater power of resistance; and the size of 
the drop will probably be influenced by the intensity of the 
electricity of the air, as well as by its dryness. The former, 
as well as the latter, will tend to increase the evaporation 
from the surface of the drop. 

It is a well-established fact, which at first sight would ap- 
pear to be at variance with the results of observations on 
towers, that a greater amount of rain falls in some cases on 
high mountains than on the adjacent plains. For example, 
the amount of water which annually falls at the convent of 
St. Bernard is nearly double that which falls at Geneva. 
This effect however is due to the south wind, loaded with 
moisture, ascending the slope of the mountain into a colder 
region, which causes a precipitation of its vapor. From what 
is here said, it will be evident that the subject of rain is one 
which involves many considerations, and which still pre- 
sents a wide field for investigation. 

A series of observations has been commenced at the Smith- 
sonian Institution on the quantities of rain at different ele- 
vations, as well as on gauges of different sizes and forms, 
the results of which will be given in one of the meteorologi- 
cal reports. 



6 WBITINGS OF JOSEPH HEKBT. [1855- 



MKTEOBOLOGY IN ITS CONNECTION WITH AGRICULTTJBE. 

PART I.— GENERAL CONSIDERATIONS. 

(Agricultural Report of Commissioner of Patents for 1855, pp. 857-874.) 

• 

All the changes on the surface of the earth, and all the 
movements of the heavenly bodies, are the immediate re- 
sults of natural forces acting in accordance with established 
and invariable laws ; and it is only by that precise knowl- 
edge of these laws, which is properly denominated science, 
that man is enabled to defend himself against the adverse 
operations of nature, or to direct her innate powers in ac- 
cordance with his will. At first sight, meteorology might 
appear to be an exception to this general proposition, and 
the changes of the weather and the peculiarities of climate 
in different portions of the earth's surface to be of all things 
the most uncertain and furthest removed from the dominion 
of law; but scientific investigation establishes the fact that 
no phenomenon is the result of accident, nor even of fitful 
volition. 

The modern science of statistics has revealed a perma- 
nency and an order in the occurrence of events depending 
on conditions in which nothing of this kind could have been 
supposed. Even those occurrences which seem to be left to 
the free will, the passion, or the greater or less intelligence 
of men are under the control of laws — fixed, immutable, and 
eternal. No one knows the day nor hour of his own death, 
and nothing is more entirely uncertain in a given case of ex- 
pected birth, than whether a boy or girl shall be born; but 
the number out of a million of men living together in one 
country who shall die in ten, twenty, forty, or sixty years, 
and the number of boys and girls who shall be born in a 
million of births, may be predicted from statistical data with 
almost unerring precision. The statistics of courts of justice 
have disclosed the astonishing fact, — incomprehensible to our 
understanding because we do not know the connecting in- 
fluences which concur to produce the result, — that in every 



-1859] WRITINGS OP JOSEPH HENRY. 7 

large country the number of crimes, as well as each kind of 
crime, can be foretold for every coming year with the same 
certainty as the number of births and deaths. Of every 
hundred persons accused before the supreme tribunal in 
France, sixty-one are condemned; in England, seventy-one; 
the variation on an average from these numbers hardly 
amounting to a hundredth part of the whole. Not only the 
number of suicides in general for several years to come can 
be foretold with confidence, but also the relative proportion 
by firearms and by hanging. 

The astonishing facts of this class lead us inevitably to 
the conclusion that all events are governed by a Supreme In- 
telligence, who knows no change, and that under the same 
conditions, the same results are invariably produced. If the 
conditions however are permanently varied, a corresponding 
change in the results will be observed ; for example, the 
effect of the introduction of an extended system of moral 
education, in diminishing crime, would be revealed by the 
statistics. 

It is this regularity observable in phenomena when 
studied in groups of large numbers, which enables us to 
arrive at permanent laws in regard to meteorology, and 
hence to predict with certainty the average temperature of 
a given place for a series of decades of years, and which fur- 
nishes the basis (in accordance with the principles of insur- 
ance) of a knowledge of what species of plant or animal 
may be profitably raised in a given locality. We need not 
however in this branch of knowledge, as in that of the sta- 
tistics of crime, be confined to the mere discovery of the ex- 
istence and the measure of the constants of nature ; but 
uniting the results of observations with those of experiments 
in the laboratory and mathematical deductions from astro- 
nomical and other data, we are enabled not only to refer 
the periodic changes to established laws, but also to trace to 
their source various perturbing influences which produce the 
variations from the mean, and thus arrive at an approximate 
explanation at least, of the meteorological phenomena which 
are constantly presented to us. 



8 WRITINGS OF JOSEPH HENRY. [185S- 

No truth is more itiiportant in regard to the material well- 
being of man, and none requires to be more frequently en- 
forced upon the public mind, than that the improvement 
and perfection of art depends upon the advance of science. 
Although many processes have been discovered by accident, 
and practiced from ago to ago without a knowledge of the 
principles on which they depend, yet as a general rule such 
processes are imperfect, and remain, like Chinese art, for 
centuries unchanged or unimproved. They are generally 
wasteful in labor and material, and involve operations which 
are not merely unessential, but actually detrimental. The 
dependence of the improvement of agriculture upon the ad- 
vance of general science, and its intimate connection with 
meteorology in particular, must be evident when we reflect 
that it is the art of applying the forces of nature to increase 
and improve those portions of her productions which are 
essential to the neccssitv and comfort of the human race. 

Modern science has established, by a wide and careful in- 
duction, the fact that plants and animals consist principally 
of solidified air, the only portions of an earthy character 
which enter into their composition being the ashes that re- 
main after combustion. All the other parts were origi- 
nally in the atmosphere, were absorbed from the mass of air 
during the growth of the plant or animal, and are given 
back again to the same fountain from which they were drawn, 
in the decay of the vegetable, and in the breathing and 
death of the animal. 

The air consists of oxygen, nitrogen, carbonic acid, the 
vapor of water, traces of ammonia, and of nitric acid. A 
young plant placed in the free atmosphere and. exposed to 
the light of the sun, gradually increases in size and weight 
by constantly receiving carbon from the carbonic acid of the 
air, which being thus decomposed, evolves the liberated oxy- 
gen. The power by which this decomposition is produced 
is now known to be due to the solar ray, which consists of a 
peculiar impulse or vibration, propagated from the distant 
sun, through a medium filling all space. 

It is a principle of nature that power is always absorbed 



-1859] WBITINGa OF JOSEPH HENRT. 9 

in producing a change in matter. This change may be per- 
manent, or it may be of such a character as to re-produce the 
power which was expended in eflfecting it. For example, 
the moving power of a cannon ball is permanently expended 
in passing into the side of a ship; but if the same ball were 
shot into the mouth of another cannon, and made to com- 
press a spring, the recoiling of the latter would give to the 
ball, in an opposite direction, precisely the same velocity 
which it had expended in compressing the spring, suppos- 
ing nothing lost by friction, &c. This example serves to 
illustrate the effect of the impulse from the sun. It decom- 
poses the carbonic acid which surrounds the leaf of the 
plant, or in other words, overcomes the natural attraction 
between the carbon and the oxygen of which the acid is 
composed, and in this effort the motions of the atoms of the 
aetherial medium are themselves stopped. The power how- 
ever in this case is not permanently neutralized, for when 
the plant is consumed, either by rapid combustion or by 
slow decay, — that is, when the carbon and the oxygen are 
again suffered to rush into union to form carbonic acid, — the 
same amount of power is evolved in the form of light, heat, 
or nervous force which was absorbed in the original compo- 
sition. If the plant moreover be consumed in the animal, 
the same power is expended in building up the organiza- 
tion, in producing locomotion, and the incessant action of 
the heart, and the other involuntary movements necessary 
to the vital process. 

Plants are therefore the recipients of the power of the sun- 
beam. They transfer this power to the animal, and the 
animal again returns it to celestial space, whence it ema- 
nated. To properly so direct this power of the sun-beam 
that no part of it may run to waste, or be unproductive of 
economical results, it is essential that we know something 
of its nature; and the lifetime of labor of many individuals, 
supported at public expense, would be well applied in ex- 
clusive devotion to this one subject. The researches which 
have been made in regard to it have developed the fact that 
the impulses from the sun are of at least four different char- 



10 WRITINGS OF JOSEPH HENBT. [18SS- 

acters, namely, the lighting impulse, the heating impulse, the 
chemical impulse, and the phosphorogenic impulse; and it 
has further been ascertained that though each of these im- 
pulses may produce an eflTect on the plant, the decomposition 
of the carbonic acid is mainly due to the chemical action. 
A series of experiments is required to determine the various 
conditions under which these impulses from the sun may 
be turned to the greatest amount of economical use, and 
what modifications they may demand, in order to the 
growth of peculiar plants. It has not yet been clearly ascer- 
tained whether some of these emanations cannot be ex- 
cluded with beneficial result, or in other words, whether 
they do not produce an antagonistic eflect; nor is it known 
what relative proportions of them are absorbed by the at- 
mosphere, or reflected from our planet by the floating clouds 
of the air, without reaching the earth. To determine these 
facts requires a series of elaborate experiments and accurate 
observations. 

We have said that the chemical vibration is that which 
principally decomposes the carbonic acid in the growth of 
the plant; but we know that the heating impulse is an aux- 
iliary to this, and that heat and moisture are essential ele- 
ments in the growth of vegetation. The small amount of 
knowledge we already possess of the character of the emana- 
tions from the sun has been turned to admirable account 
in horticulture. In this branch of husbandry we seek — 
even more than in agriculture — ^to modify the processes of 
nature; to cultivate the plants of the torrid zone amid the 
chilling winds of the northern temperate zone, and to render 
the climate of sterile portions of the earth congenial to the 
luxurious productions of more favored regions. We seek 
to produce artificial atmospheres, and to so temper the im- 
pulses from the sun that the eSbcts of variations in latitude 
and the rigor of the climate may be obviated. 

From all that has been said therefore it will be evident 
that the hopes of the future, in regard to agriculture, rest 
principally upon the advance of abstract science, not upon 
the mere accumulation of facts, of which the connection and 
dependence are unknown, but upon a definite conception of 



-1859] WRITINGS OP JOSEPH HENRY. H 

the general principles of which these facts are the result. 
All the phenomena of the atmosphere should be studied and 
traced to the laws on which they depend. The labor be- 
stowed upon investigations of this kind is not (as the narrow- 
sighted advocate of immediate utilitarian results would 
affirm) without practical importance ; on the contrary, it is 
the basis of the highest improvement of which the art of 
agriculture is susceptible. On every acre of ground a defi- 
nite amount of solar force is projected, which may under 
proper conditions be employed in developing organization ; 
and the great object of the husbandman is to so arrange the 
conditions, that the least possible amount of this may be lost 
in un-economical results. Independently however of the 
practical value of a knowledge of the principles on which the 
art of agriculture depends, the mind of the farmer should be 
cultivated as well as his fields, and after the study of God's 
moral revelation, what is better fitted to improve the intel- 
lect than the investigation of the mode by which He pro- 
duces the changes in the material universe ? 

The climate and productiveness of a country are deter- 
mined, first, by its latitude, or its distance on either side of 
the equator; second, by the configuration of the surface as 
to elevation and depression ; third, by its position, whether 
in the interior of a continent or in proximity to the ocean ; 
fourth, by the direction and velocity of the prevailing winds ; 
fifth, by the nature of the soil ; and lastly, by the cultiva- 
tion to which it has been«subjected. 

First, in regard to latitude : The productive power of a 
soil (other things being the same) depends on two circum- 
stances, — solar radiation and moisture ; and these increase 
as we approach the equator. 

If the kind of food were a matter of indifference, the same 
extent of ground which supports one person at the latitude 
of 60° would support twenty -five at the equator ; but the 
food necessary to the support of persons in different lati- 
tudes varies with respect to quality as well as to quantity; 
and the other conditions mentioned, with regard to climate, 
should enter largely into the estimate we form in relation 
to the actual productiveness of different parallels of latitude. 



12 WRITIKGS OF JOSEPH HSNBY. [18W- 

Though some of the heat of the san is absorbed in its 
passage through the atmosphere, yet by far the greater por- 
tion (particularly at the equator) arrives at the surface of 
the earth, is absorbed by the soil, and is imparted to the 
stratum of air in contact with it From various determi- 
nations it is a well-established fieict that the temperature of 
celestial space beyond our atmosphere is at least 50^ below 
the zero of Fahrenheit's scale. The upper surface of the 
atmosphere and the Arctic regions must therefore partake of 
this low temperature, while that of the lower stratum at the 
surface of the earth is at the equator about 80^. The air 
therefore diminishes in temperature as we ascend, but the 
rate of this diminution varies within certain limits in differ- 
ent parts of the earth ; and to settle the law of diminution 
definitely, a series of observations by means of ascents in 
balloons will be required. For practical purposes however 
we may assume in the temperate zone that the diminution 
due to altitudes or mountains is about 1° of Fahrenheit for 
300 feet. Furthermore, as we ascend and the pressure of 
the superincumbent strata is thus reduced, the air becomes 
lighter; and though the temperature of the several por- 
tions diminishes very rapidly, yet the whole amount of heat 
in each pound of air is very nearly the same. For ex- 
ample, if a certain weight of air were carried from the sur- 
face of the earth to such a height that it would expand into 
double its volume, the heat which it contained would then 
be distributed throughout twice the space, and the tempera- 
ture would consequently be much diminished, though the 
absolute amount of heat would be unchanged. If the same 
air were returned to the earth whence it was taken, conden- 
sation would ensue, and the temperature would be the same 
as at first. 

2. On this principle a wind passing over a high mountain 
is not necessarily cooled ; for the diminution of temperature 
which is produced by the rarefaction of the ascent would be 
just equivalent to the increase which is due to the conden- 
sation in an equal descent. This would be the case if the 
air were perfectly dry ; but if it contained moisture, para- 



-1859] WRITINGS OF JOSEPH HENRY. 13 

doxical as it may seem, it would be warmer when it re- 
turned to the lower level than when it left it. In ascending 
to the top of the mountain it would deposit its moisture in 
the form of water or snow, and the "latent heat" given out 
from this, would increase the heat of the air; and when it 
descended on the opposite side to the same level from which 
it ascended^ it would be warmer on account of this addi- 
tional heat. The configuration of the surface of our con- 
tinent has on this account therefore a marked influence on 
the temperature of its different parts. 

3. The effect on its climate, of the position of a country, 
as regards its proximity to the ocean, will be evident from 
the facts relative to the radiation and absorption of heat by 
different substances. All bodies on the surface of the earth 
are constantly receiving and giving out heat. A piece of 
ice exposed to the sun sends rays to this luminary, and re- 
ceives in return a much greater amount. The power how- 
ever of radiating and receiving heat is very variable in 
different bodies. Water exposed to the same source of heat 
receives and radiates in a given time far less than earth ; 
consequently the land (especially in the higher latitudes) 
during the long summer days or during the growing season, 
receives much more heat than the corresponding waters of 
the same latitude ; and though the radiation at night is 
less from the water than the land, yet the accumulating in- 
crease of temperature of the latter will be much greater 
than that of the former. The reverse takes place in the 
winter. While therefore the mean temperature of the ocean 
and of the land in the same latitude may remain the same, 
the tendency of the land is to receive the greater portion 
of the heat of the whole year during the months of summer, 
and thus, by a harmonious arrangement with respect to the 
production of organic life, to increase the effect of the solar 
radiation, and to widen the limits within which plants of a 
peculiar character may be cultivated. 

Proximity to the sea however has another effect on the 
climate, which depends upon the currents of the former, by 
which the temperature of the earth due to the latitude is 



14 WRITINGS OF JOSEPH HENRY. [1855- 

materially altered. Heated water is constantly carried from 
the equatorial regions towards the. poles, and streams of cold 
water returned, by means of which the temperature of the 
earth is modified and the extremes reduced in intensity. The 
great currents of the ocean are seven in number, and may 
be best and most clearly described in connection with an 
hypothesis as to their origin. For this purpose let us sup- 
pose the earth at rest and the equatorial regions continually 
heated by the sun. In this condition a continuous current 
of air from the north and another from the south would 
blow towards the equator, there ascend and flow backward 
in the upper regions towards the poles. If wo next suppose 
the earth to be in motion on its axis from west to east, and 
compound the effects of this motion with that of the winds 
towards the equator on either side, they will not meet di- 
rectly opposite each other, as in the previous supposition, 
but at an acute angle, and produce a belt of wind from east 
to west entirely around the earth in the region of the equator. 
The continued action of this wind on the surface of the 
water would evidently give rise to a current of the ocean in 
the belt over which the wind passed. If now instead of 
considering the earth entirely covered with water, we sup- 
pose the existence of two continents extending from north to 
south, forming barriers across the current we have described, 
and establishing two separate oceans, similar to the Atlantic 
and Pacific, then the continuous current to the west would 
be deflected right and left or north and south at the western 
shore of each ocean, and would form four immense whirlpools, 
namely, two in the Atlantic, one north and the other south 
of the equator, and two in the Pacific, similar in situation 
and direction of motion. The regularity of the outline of 
these whirls will be disturbed by the configuration of the 
deflecting coasts, and the form of the bottom of the sea, as 
well as by islands and irregular winds. For a like reason 
a similar whirlpool will tend to be produced in the Indian 
Ocean, the current from the east being deflected down the 
coast of Africa, and returning again into itself. along a 
southern latitude on the western side of Australia. A fifth 



-1859] WRITINGS OP JOSEPH HENRY. 15 

whirl exists in this ocean, and in some seasons is at times 
divided into two, giving rise to the peculiar currents of this 
part of t he earth's surface. Besides these great circular 
streams, the water supplied by all the rivers emptying into 
the Arctic basin, as well as that from all the precipitation 
in this region, returns to the south in a current between 
Europe and America^ which as we shall hereafter see has 
a very marked influence on the temperature of our coast. 
A similar current, but more diffuse and less in amount, must 
constantly flow from the Antarctic regions. In this view 
we have adopted the hypothesis which ascribes the principal 
effect to the trade winds. A portion however will be duo 
to the currents produced by the heating of the water itself. 
To illustrate the effect of these currents on the climate of 
the United States, let us consider those of the North Atlantic 
and North Pacific oceans, between which our continent is 
situated. 

The great whirl in the North Atlantic, the western and 
northern portions of which are known as the Gulf Stream, 
passes southward down the coast of Africa, crosses the ocean 
in the r^ion of the equator, is deflected from the northern 
portion of South America and the coast of Mexico along the 
United States, and re-crosses the Atlantic at about the lati- 
tude of 40°, to return into itself at the place where it started. 
A portion however of this current (probably owing to the 
configuration of the bottom) passes oflf in a tangent to the 
circumference of the great whirl and flows northward along 
the coasts of Ireland and Norway. By this current the 
heated waters of the equator are carried northward along the 
eastern coast of the United States and precipitated upon the 
shores of Northern Europe, giving the temperature of a south- 
ern latitude even to North Cape, the extremity of Europe, 
which would otherwise be as cold as Greenland. This stream 
has less effect upon the climate of the United States than 
upon tjiat of the western coast of Europe; first, because the 
prevailing wind is from the west; and secondly, because be- 
tween our shores and the Gulf Stream the cold polar current 
intervenes. 



16 WRITINGS OF JOSEPH HENRY. [1855- 

In the North Pacific Ocean, on the western side of our 
continent, the great circle of water passes up along the coast 
of Japan, re-crosses the ocean in the region of the Aleutian 
Islands, mingles with the fitful current outward through 
Behring's Strait, and thence down along the northwest coast 
of North America. In this long circuit the northeastern 
portion of it is much more cooled than the similar portion 
of the whirl of the Atlantic. It therefore modifies the tem- 
perature of the northwestern coast and produces a remark- 
able uniformity along its whole extent, from Sitka to the 
southern extremity of California. It is an interesting fact, 
which we have just derived from Captain John Rodgers, that 
an offshoot from the great whirl in the Pacific, analogous to 
that which impinges on the coast of Norway, enters along 
the eastern side of Behring*s Strait, while a cold current 
passes out on the western side, thus producing almost as 
marked a difference in the character of the vegetation on 
the two shores of the strait as between that of Ireland and 
Labrador. 

4. The effect of prevailing currents of air on the climate of 
different portions of the earth is no less marked than that 
of proximity to the sea. We have seen that on one side of a 
line over which the sun passes, a current of air flows from 
the northeast, and on the other from the southeast, giving 
rise to the trade winds. These winds ascend obliquely, and 
according to the views of Dove and others, rise to the upper 
regions of the atmosphere, flow backward towards the poles, 
and partaking of the rotary motion of the earth, gradually 
turn 4,0 the eastward and approach its surface, producing a 
scries of whirls overlapping each other entirely around the 
globe. Whatever may be the cause however of the phe- 
nomena. Professor CoflBn, in his admirable paper on the 
winds of the northern hemisphere, has shown that from the 
equator to the pole the whole space is occupied by three 
great belts, or zones, of prevailing wind: the first extends 
from the equator to an average latitude of 35° north, in 
which the current is from the northeast, constantly growing 
less intense as we approach the northern limit ; the second 



-1859] WRITINGS OF JOSEPH HENRY. 17 

is that from 35*^ to about 60°, the current from the west be- 
ing more intense in the middle of the belt, and gradually 
diminishing on either side almost into a calm; third, from 
60° to the pole, or rather to a point of greatest cold in the 
Arctic regions, the wind is in a northeasterly direction. 

The first of these belts would constitute what is called the 
trade winds, produced as we have said, by the combined ef- 
fects of the heat of the sun and the rotation of the earth ; 
the second is the return trade, and the third the current 
which would be produced by an opposite eflfect to that of the 
rarefaction of the air by the sun at the equator, namely, the 
condensation of the air by the cold portion of the earth. 
The air should flow out in every direction from the coldest 
point, and combining its motion towards the south with 
the rotation of the earth, it should take a direction from 
the east to the west or become a northeasterly wind. 

The eflfects which these currents must have upon the 
climate of the United States will be made clear by a little 
reflection. The trade winds within the tropics, charged with 
vapor, in their course towards the west impinging upon the 
mountainous parts of South America, will deposit their 
moisture on the eastern slope and produce a rainless district 
on the western side. Again, a lower portion of the Atlantic 
and Gulf trade wind will be deflected from these mountains 
along the eastern coast of the United States and through 
the valley of the Mississippi as a surface wind, and thus 
give rise to our moist and warm summer breezes from the 
south, while the principal or upper portion of the trade 
wind (or the return westerly current) sweeping over the Pa- 
cific Ocean, and consequently charged with moisture, will 
impinge on the Coast Range of mountains of Oregon and Cal- 
ifornia, and in ascending its slopes deposit moisture on the 
western declivity, giving fertility and a healthful climate to 
a narrow strip of country bordering on the ocean and steril- 
ity to the eastern slope. All the moisture however will not 
be deposited in the passage over the first range, but a por- 
tion will be precipitated on the western side of the next, 
until it reaches the eastern elevated ridge of the Rocky 

2-2 



5 



18 . WRITINGS OF JOSEPH HENRY. [1855- 

Mountain system, where we think it will be nearly, if not 
quite, exhausted. East of this ridge, and as it were, in its 
shadow, there will exist a sterile belt, extending in a north- 
erly and southerly direction many hundred miles. The 
whole country also included between the eastern ridge of 
the Rocky Mountains and the Pacific Ocean, with the ex- 
ception of the narrow strip before mentioned, will be de- 
ficient in moisture, and on account of the heat evolved (as 
before shown) by the condensation of moisture on the ridges, 
will be at a much higher temperature than that due to lat- 
itude. This mountain region and the sterile belt east of it 
occupy an area about equal to one-third of the whole sur- 
face of the United States, which with our present knowledge 
of the laws of nature and their application to economical 
purposes must ever remain of little value to the husbandman. 
According to this view, the whole valley of the Mississippi 
owes its fertility principally to the moisture which proceeds 
from the Gulf of Mexico, and the inter-tropical part of the 
Atlantic Ocean. The Atlantic Gfulf Stream therefore (as 
already remarked) produces very little effect in modifying 
the climate of the northern portion of the United States; 
both on account of the cold polar current which intervenes 
between it and the shore, and because of the prevalent west- 
erly wind, which carries the heat and moisture from us, 
and precipitates them on the coast of Europe. 

5. The influence of the nature of the soil on the climate 
of a country, may be inferred from its greater or less power 
to absorb and radiate heat, and from its capacity to absorb, 
or transmit over its surface, the water which may fall upon 
it in rain, or be deposited in dew. In the investigation of 
this part of the subject, the observations of the geologist, 
and the experiments of the chemist and the physicist must 
be called into requisition. 

6. In regard to the influence of cultivation on the climate 
of a country much also may bo said, though at first sight 
it might appear that man, with his feeble powers, could hope 
to have no influence in modifying the action of the great 
physical agents which determine the heat and moisture of 



-i859] WRITINGS OP JOSEPH HENRY. 19 

any extended portions of the globe. But though man can- 
not (Jirectthe winds, nor change the order of the seasons, he 
is enabled, by altering the conditions under which the forces 
of nature operate, materially to modify the results produced ; 
for example, removing the fore^sts from an extended portion 
of country exposes the ground to the immediate radiation 
of the sun, and increases in many cases the amount of 
evaporation ; in other places it bakes the earth and allows 
the water to be carried oflF to the ocean in freshets, and in 
some instances, in destructive inundations. 

Drying extensive marshes, or the introduction of a general 
system of drainage, has a remarkable influence in modifying 
the temperature. The water which would evaporate, and 
by the latent heat thus absorbed, would cool the ground, is 
suflFered to pass through it to the drain beneath, and is thus 
carried oflF without depriving the earth of a large amount 
of heat, which would otherwise be lost. Besides this, the 
removal of forests gives greater scope to the winds, which 
are hence subjected to less friction in their passage over the 
earth. 

The whole subject of the removal of forests is one which 
deserves more attention than it has usually received. In 
the progress of settlement, it is evident that a great portion 
of the wooded land of a now country must give place to the 
cleared field, in order that man may reap the rich harvest 
of the cereals, which in his civilized condition are necessa- 
ries as well as luxuries of life; yet the indiscriminate 
destruction of the forests is of doubtful propriety. By the 
judicious reservation of trees along the boundaries of cer- 
tain portions of land, in accordance with the known direc- 
tion of the prevailing wind, the climate may be ameliorated 
within a restricted portion of the earth, both for the pro- 
duction of plants and animals. While in some parts of the 
country the clearing of nearly all the ground is absolutely 
necessary for agricultural purposes, in others it may be 
profitable to allow forests of considerable extent to remain 
in their pristine condition. Cases of this kind however can 
be determined only by the particular climate of each district 
of the country. 



20 WRITINGS OF JOSEPH HENRY. [1855- 

It is now an established truth that certain localities are 
screened from miasmatic influence b)' the intervention of 
trees. A more general recognition of this fact might add 
much to the healthfulness of localities in other respects 
highly desirable. 

The solar rays, in passing through the atmosphere, do not 
heat it in any considerable degree, but they heat the earth 
against which they impinge; therefore the temperature of 
the lower stratum of ait is derived, directly or indirectly, 
from the soil on which it rests; and this temperature, as 
has been remarked, will depend upon whether the surface 
be marshy or dry, clothed with herbage, or covered with 
sand, clay, or an exposed rock. From this fact it is evident 
that man has, in this particular also, considerable power in 
modifying the climate of portions of the earth; and history 
furnishes us with many examples in which great changes, 
within human control, have been produced in the course of 
ages. Nineveh and Babylon, once so celebrated for their 
advance in civilization and opulence, and Palmyra and Baal- 
bec, for their magnificence, ofler at this daj*^ to the traveller 
the site of ruins which attest their past greatness, in the 
midst of desolation. Canaan, described in the Bible as a 
fertile country, "flowing with milk and honey," is now 
nearly deprived of vegetation, and presents a scene of almost 
uninterrupted barrenness. The climate of these countries 
is undoubtedly modified by the present st^ite of the surface, 
and might again be ameliorated by cultivation, were the 
encroachments of the sands of the desert stayed by borders 
of vegetation of a proper character. Many parts, even of 
our own country, which now exhibit a surface of uninter- 
rupted sand, may be rendered productive, or covered with 
trees and herbage. 

A series of observations on the progress of temperature 
below the surface, in different parts of the country, and even 
in different fields of the same plantation, would be of value 
in ascertaining the proper time to introduce the seed, in 
order that it might not be subjected to decay by premature 
planting, or lose too much of the necessary influence of 



-1859] WRITINGS OP JOSEPH HENRY. 21 

summer by tardy exposure in the ground. This may per- 
haps bo most simply effected by burying a number of bot- 
tles filled with water at different depths in the ground, say 
one at the depth of 6 inches, another at 12, and a third at 
18 inches- These in the course of time would take the 
temperature of the earth in which they were embedded, and 
would retain it sufficiently long unchanged, to admit of its 
measurement, by inserting a thermometer into the mouth 
of the bottle. 

No improvement is more necessary, for rendering the art 
of agriculture precise, than the introduction into its pro- 
cesses of the two essential principles of science, namely, 
those of weight and of measure. All the processes in our 
manufactories, on a great scale, which were formerly con- 
ducted by mere guesses, as to heat and quantities, are now 
subjected to rules, in which the measure of temperature and 
the weight of materials are definitely ascertained by reliable 
instruments. 

The foregoing are general views as to the great principles 
which govern the peculiarities of climate, and especially 
that of the United States, the truth of which, in reference to 
our continent, and the modifications to which they are to 
be subjected, are to be settled by observations in the future. 

In order however that the science of meteorology may 
be founded on reliable data, and attain that rank which its 
importance demands, it is necessary that extended systems 
of co-operation should be established. In regard to climate, 
no part of the world is isolated ; that of the smallest island in 
the Pacific is governed by the general currents of the air and 
of the waters of the ocean. To fully understand therefore 
the causes which influence the climate of any one country, 
or any one place, it will be necessary to study the condi- 
tions, as to heat, moisture, and the movements of the air of 
all others. It is evident also that, as far as possible, one 
method should be adopted, and that instruments affording 
the same indications, under the same conditions, should be 
employed. 

It is true that, for determining the general changes of 



22 WRITINGS OP JOSEPH HENRY. [1855- 

temperature, and the great movements of the atmosphere 
of the globe, comparatively few stations of observation, of 
the first class, are required ; but these should be properly 
distributed, well furnished with instruments, and supplied 
with a sufficient corps of observers, to record at all periods 
of the day the prominent fluctuations. Such stations how- 
ever can only be established and supported by the co-opera- 
tion of a number of governments. 

A general plan of this kind for observing the meteoro- 
logical and magnetical changes more extensively than had 
ever before been undertaken, was digested by the British 
Association in 1838, in which the principal governments of 
Europe were induced to take an active part; and had that of 
the United States and those of South America joined in 
the enterprise, a series of watch-towers of nature would have 
been distributed over every part of the earth. The follow- 
ing were the stations of the several observatories estab- 
lished : Those of the English Government were at Green- 
wich, Dublin, Toronto, St. Helena, Cape of Good Hope, Van 
Dieman's Land, Madras, Simla, Singapore, and Aden. The 
E'ai!sian observatories were at Boulowa, Helsingfors, Peters- 
burg, Sitka, Catherineburg, Kasan, Barnaoul, NicolaieflF, 
Nertschinsk, Tiflis, and Pekin. Those of Austria were at 
Prague and Milan. In the United States, an observatory 
was established at Girard College, under the direction of 
Professor Bache. The French Government had one at Al- 
giers; the Prussian Government, one at Breslau; the Bava- 
rian Government, one at Munich; and the Belgian, one at 
Brussels. There was one at Cairo, supported by the Pasha 
of Egypt, and one in India, at Travandrum. 

These observatories were established to carry out a series 
of observations at the same moment of absolute time, every 
two hours, day and night, during three years, together with 
observations once every month, continuing 24 hours, at in- 
tervals of five minutes each. They were all furnished with 
standard instruments, and followed instructions adopted by 
the directors of the general system. Operations were com- 
menced in 1839, and in a number of cases, were continued 



-1859] WRITINGS OF JOSEPH HENRY. 23 

through nine years. The number of separate observations 
amounted to nearly six millions, which required at least as 
much labor for their reduction as that expended in the ob- 
servations themselves. The comparisons of these observa- 
tions are still in progress, and will occupy the attention of 
the student of magnetism and meteorology for many years 
to come. The system was established more particularly to. 
study the changes of the magnetic needle, and on this sub 
ject alone it has aflfbrded information of sufficient impor- 
tance to repay all the- labor and time expended on it. It 
has shown that the magnetic force is scarcely constant from 
one moment to another, that the needle is almost incessantly 
in motion, that it is aflFected by the position of the sun and 
moon, and by perturbations, connected with meteorological 
phenomena, of a most extraordinary character. 

In regard to meteorology, this system furnished reliable 
data for the great movements of the atmosphere, and the 
changes in its thermal and hygrometric condition. But to 
obtain a more minute knowledge of the special climatology 
of diflferent countries, it is necessary that a series of observa- 
tions, at a great many places, should be continued through 
a number of years, and at stated periods of the day — not as 
frequent as those of the observations we have mentioned, 
but embracing as many elements, and even adding to these, 
as new facts may be developed or new views entertained. 
In many countries accordingly, provision has been made by 
their respective governments, for continued though local sys- 
tems of this kind. The Government of Prussia appears to 
have taken the lead in this important labor, and its example 
has been followed by those of Great Britain, Russia, Austria, 
Bavaria, Belgium, Holland, and France. In these coun- 
tries, regular and continuous observations are made with 
reliable instruments, on well-digested plans. 

Though the Government of the United States took no part 
with the other nations of the earth in the great system be- 
fore described, yet it has established and supported for a 
number of years a partial system of observation at the dif- 
ferent military posts of the army. Among other duties 



24 WRITINGS OF JOSEPH HENRT. [1855- 

ossigned to the surgeons, at the suggestion of Surgeon Gen- 
eral Lovell, was that of keeping a diary of the weather, and 
of the diseases prevalent in their vicinity. The earliest reg- 
ister received, under this regulation, was in January, 1819. 
The only instruments at first used were a thermometer and 
wind-vane, to which in 1836, a rain-gauge was added. The 
observations were made at 7 a. m. and 9 p. m., and the winds 
and weather were observed morning, noon, and evening. It 
is to be regretted that in 1841, the variable hour of sunrise 
was substituted for that of 7 a. m., since the latter admits of 
an hourly correction which cannot be applied to the former, 
except at the expense of too great an amount of labor. 

The results of the observations for 1820 and 1821 were 
published at the end of each year ; those from 1822 to 1825, 
inclusive, were issued in the form of a volume by Surgeon 
(ieneral Lovell ; those from 1826 to 1830, and from 1830 to 
1842, inclusive, were prepared and published in two vol- 
umes, under the direction of the present Surgeon General, 
Dr. Thomas Lawson. At the commencement of 1843 an 
extension of the system was made by the introduction of 
now instruments, and an additional observation to the num- 
ber which had previously been recorded each day, and hourly 
observations for twenty-four hours were directed to be taken 
at the equinoxes and solstices. 

During the past year a quarto volume has been published, 
which contains the results of the observations of the ther- 
rijoriKiter, direction and force of winds, clearness of sky, and 
full of niin and snow, during a period of twelve years, from 
thrj first of January, 1843, to January, 1855, arranged in 
iiiontlily tables and annual summaries. To these are added 
conHoli(lut(i(l tables of temperature and rain for each separate 
nUition, comprising the results of all the thermometric ob- 
Hf',rvid'u)UH made by medical officers since 1822, and of all 
tiu*nH\iri*AnoA\iH of rain and snow since the introduction of 
tJM? niin-^au^o in 1830. 

TIk; tubular part of this volume contains the most irapor- 
liint rr?HultH of the observations of the army system of regis- 
imtion, and will bo considered the most valuable contribu- 



-1855] WRITINGS OP JOSEPH HENRY. 25 

tion yet made toward a knowledge of the climatology of the 
United States. Truth however will not permit us to express 
the same opinion in reference to the isothermal charts which 
accompany this volume. These we consider as premature 
publications, constructed from insufficient data, and on a 
principle of projection by which it is not possible to repre- 
sent correctly the relative temperatures in mountainous 
regions. 

With the learning and zeal for science possessed by the 
officers of the United States army, and the importance 
which they attach to meteorology, in its connection with 
engineering and topography, it is hoped that this system 
may be further extended and improved, that each station 
may be supplied with a compared thermometer and psy- 
chrometer, and that at a few stations a series of hourly ob- 
servations may be established, for at least a single year. 
The present Secretary of War, we are assured, would will- 
ingly sanction any proposition for the improvement of this 
system, and we doubt not the Surgeon General is desirous 
of rendering it as perfect as the means at his disposal will 
permit. 

A local system of meteorological observations was estab- 
lished in the State of New York in 1825, and has been unin- 
terruptedly conducted from that time until the present. 
Each of the academies which participated in the literature 
fund of the State was furnished with a thermometer and 
rain-gauge, and directed to make three daily observations 
relative to the temperature, the direction of the wind, cloud- 
iness, &c. The system was re-modeled, in 1850, so as to 
conform to the directions of the Smithsonian Institution, 
and a considerable number of the academies were furnished 
with full sets of compared instruments, consisting of a barom- 
eter, thermometer, psychrometer, rain-gauge, and wind-vane. 

A summary of the results of the observations from 1826 
to 1850, inclusive, has just been published by the State of 
New York, under the direction of the regents of the Uni- 
versity. They are presented in the form of a quarto vol- 
ume, to which is prefixed a map of the State, showing the 



26 



WRITINGS OP JOSEPH HENRY. [laSS- 



direction of the wind and the position of each station. This 
volume, the computations for which were made by Dr. 
Frankhn B. Hough, is also a valuable contribution to me- 
teorology, and does much credit to the intelligence and per- 
severance of those who introduced and have advocated the 
continuance of this system, and to the liberality of the State 
which has so long and so generously supported it. 

A system of State observations in Pennsylvania was estab- 
lished in 1837. For this purpose the Legislature appropri- 
ated $4,000, which sum was placed at the joint disposal of 
a committee of the American Philosophical Society and the 
Franklin Institute. The results of this system have not yet 
been presented to the world in a digested form. 

Another State system was established in Massachusetts in 
1841), tlio records of wliich have been presented to the Smith- 
Honian Institution, and will be published, in considerable 
detail, cither at the expense of the State or of the Smithson- 
ian fund. 

A system of meteorological observations was established 
by the Smithsonian Institution in 1849, the principal object 
of which was to study the storms that visit the United States, 
particularly during the winter months. This system, which 
luiH been continued up to the present time, was afterward 
extended, with a view to collect the statistics necessary to 
ascertain the character of the climate of North America, to 
(l(;t<jrmine the average temperature of various portions of the 
(country, and the variations from this at diflferent periods of 
tli(5 year. It was intended to reduce, as far as possible, the 
w;v(!nil systems of observations to one general plan which 
had previously been established, and to induce others to 
i?ng/ige in the same enterprise. But in order that the results 
ini^lit b(j comparable with those obtained in other countries, 
it wuH HJgarded as of primary importance that the instruments 
hIioiiM b(; more accurate than those which might be requi- 
mUi for the mere determination of the phenomena of storms. 
Tim hiMtitution therefore procured standard barometers and 
tlMjfiriornijtijrH from London and Paris, and with the aid of 
VntfuHHOT Ouyot, a distinguished meteorologist, copies of 



-1859] WRITINGS OP JOSEPH HENRY. 27 

these were made, with improvements, by Mr. James Green, 
a scientific artisan, of New York. A large number of these 
instruments have been constructed and sold to observers. 
Full sets have been furnished by the Institution to parties 
in important positions, and in some cases, half the cost has 
been paid from the Smithsonian fund. 

A growing taste having been manifestly created for the 
study of practical meteorology, directions for observations 
and a volume of tables for their reduction, have been pre- 
pared and widely circulated at the expense of the Institu- 
tion. It has also distributed blanks to all the observers of 
the diflerent systems alluded to, except those of the army, 
and has received in return, copies of all the observations 
which have been made. It has in this way accumulated a 
large amount of valuable material relative to the climate of 
this country and to the character of the storms to which it 
is subjected. The completeness and accuracy of the obser- 
vations have also increased from year to year ; and by an 
arrangement which the Institution has now made with the 
Patent OflSce, it is hoped that the system will be extended, 
and its character improved. 

It being manifest from the foregoing statements, and 
from other evidences, that much interest is awakened in 
this country on the subject of meteorology, it is hoped that 
the means may be afforded for reducing and publishing the 
materials which have been and may hereafter be accumu- 
lated, and that important results to agriculture, as well as 
to other arts, may be hence deduced. 

Description of the Tables* 

The numbers given in the accompanying meteorological 
tables are mostly those indicating average or mean results. 
The principle of deducing general laws from a multiplicity 
of facts or observations — ^though liable in themselves to error, 
is of the greatest value in modern science. If we observe 

* [Twenty pages of Meteorological Tables following this part are omitted 
in the present re-print.] 



28 WRITINGS OP JOSEPH HENRY. [1855- 

the temperature of a given place every hour in the day, add 
all the observations into one sum for a year, and divide by 
the number of hours in a year, we shall get the mean 
annual temperature. By this method of observation we 
shall ascertain the warmest and the coolest hours of each day, 
and by repeating the same process for a number of years, 
we shall learn the temperature of each hour, eliminated 
from all perturbations, and in this way arrive at truths which 
could not be obtained by any other means. If we examine 
the individual records we shall find the warmest time to 
recur, on different days, at different hours. We know how- 
ever that if there were no perturbing influences the warmest 
period of the day would be that at which the heat received 
from the sun is just equal to the cooling of the earth by 
radiation into space. At every instant from the rising of 
the sun previous to this the earth would be receiving more 
heat than it gave off, and hence the temperature would con- 
stantly increase until the heating and cooling were equal. 
After this the earth would give off more heat than it would 
receive; and the temperature would begin to descend. On 
individual days however, clouds may intervene, or winds of 
varying temperatures and velocities may prevail, so as to 
change the hour of maximum heat ; but as these are not 
periodical or governed by recurring laws, the probability 
is that they will act in opposite directions ; that is, on some 
days hasten the maximum period, and on other days retard 
it, and thus in the course of a year, or several years, neutral- 
ize each other. The method of averages therefore enables 
us to separate the effects produced by irregular variations 
from those which are due to permanent causes. The latter 
are called periodic variations, while to the former has been 
given the name of non-periodic. By continuing the obser- 
vations for a number of years, in ascertaining the tempera- 
ture at a given place, we find by the method we have ex- 
plained a result from which that of the individual years 
will oscillate on either side within certain limits, while for 
two separate decades of years it will scarcely differ at all ; 
and this is the mean temperature of the place. The same 



-1859] WRITINGS OP JOSEPH HENRY. 29 

statement may be made in regard to the other elements of 
meteorology, and the result of all the observations may be 
divided into two great classes, periodical and non-periodical, 
though by a very long series of observations, it may happen 
that a phenomenon which at first may appear entirely fit- 
ful, will afterwards prove to be recurring; and at all events 
the non-periodic variations are found to be restricted within 
definite limits, the maximum amount of which it is highly 
necessary to obtain. 

The first element given in the tables is that of the mean 
height of the barometer from month to month. This is 
perhaps less immediately essential to the agriculturist than 
any other meteorological element. It is however of much 
importance in determining the progress of storms and the 
area over which the commotions of the atmosphere con- 
nected with them are perceptible, though no violent dis- 
turbances may be observed. For example, if the barometer 
on a given day is higher or lower than the average for the 
month, we are then convinced that it is subjected to some 
unusual perturbation; and by drawing a line on a map 
through all the places at which a given amount of disturb- 
ance is felt at a particular time, we are enabled to trace the 
boundary of a storm, and to indicate its progress, develop- 
ment, and end. For this purpose it is not necessary even 
that the barometers should be strictly comparable with each 
other ; it is only necessary that the results should bo com- 
parable among themselves. When the barometers have 
been accurately compared with each other, (as in the case of 
those of Green, of New York, constructed under the direc- 
tion of the Smithsonian Institution,) they afford the data for 
determining the relative elevation of different places of ob- 
servation above the level of the sea. 

The indications of the barometer, compared with those of 
the hygrometer, thermometer, and wind- vane, furnish* us 
with a method of predicting changes in the weather. These 
however in many cases will be found to depend upon rules 
applicable to particular places, and which can only be de- 
termined by a long series of local observations. 



30 WRITINGS OF JOSEPH HENRY. [1855- 

The next element given in the tables is the mean monthly 
temperature. By comparing this with the average deduced 
from a number of years' observations we are enabled to 
ascertain the variations of each month from the normal 
temperature of the same month as deduced from a series 
of years, and to compare the temperature of the "growing" 
portions of diflFerent years with each other. When experi- 
ments shall have been made upon the amount and distri- 
bution of heat necessary to give the best development to 
particular plants, by a table of this kind we are enabled to 
select the months best suited to their cultivation. More- 
over, each plant require:^ a certain amount of heat for its 
proper growth, though this amount may vary considerably 
in intensity; for example, a comparatively low degree of 
heat may be compensated b)' its longer continuance. This 
rule however is confined within certain limits; for if the 
temperature rises above a given degree, or falls below a par- 
ticular point, the vitality of the plant may be destroyed. 
By a well-conducted series of experiments and observations 
the agriculturist may be enabled to determine, without a 
ruinous series of actual trials, what plant may be safely culti- 
vated in a given place. 

Besides the mean temperature, the extremes are also given, 
and these are of essential importance in determining the 
variations of temperature to which the plant is to be sub- 
jected. The length of the growing summer in a given year, 
and in a particular place, may for instance be measured by 
the interval which occurs between two killing frosts. 

The next element in order, presented in the accompany- 
ing tables, is that of the moisture; and this is of much im- 
portance in judging of the productiveness of different years 
and diflFerent places. Unfortunately however, comparatively 
few observations are regularly made on the variations of 
mbisture in the atmosphere, in the United States. It is to 
be hoped that our returns for another year will indicate an 
increased number of the stations where valuable observa- 
tions of this kind are taken. The figures in the tables do 
not indicate the actual amount of water, for example, in a 



-1859] WRITINGS OF JOSEPH HENRY. 31 

cubic foot of air, but the fractional part of the whole amount 
necessary to produce entire saturation ; thus if saturation is 
represented by 100, 57 indicates that this number of parts 
of water is contained in the air, or that it is a little more 
than half saturated. We are obliged to adopt this method 
of representation, because the relative moisture and dryness 
of the air depend upon the temperature, and not on the abso- 
lute quantity of vapor present. Thus air at 32® F., which 
contains as much water as it can hold, or in other words is 
saturated would by heating, become exceedingly dry, though 
containing absolutely the same amount of water. The rela- 
tive dryness is indicated by the complement of the numbers 
in the table, and consequently may be found by subtracting 
these numbers from 100. The state of our feelings is much 
more aflFected by the moisture of the atmosphere than by the 
temperature, and the sensation called " closeness " is princi- 
pally due to the great amount of humidity, or in other words, 
to the diminution of the dryness of the air, which prevents 
evaporation from the surface of the body, and its attendant 
cooling etiects. A series of observations oh the relative 
humidity in the regions west of the Mississippi, and the 
northern portions of the middle part of our continent, 
in connection with the different winds, would be highly in- 
teresting in determining the source of the vapor in these 
regions, as well as settling definitely the fact in regard to 
their average productiveness. 

Another element intimately connected with the moisture 
in the air, is the amount of rain and snow, particularly the 
former. Besides the whole amount which falls during a 
year, it is necessary to know the relative quantity which 
falls in diflferent months. A large amount of rain may fall 
at once, and a greater relative proportion of it will be carried 
oflF, before the earth can have time to be fully saturated 
through the streams of creeks and rivers, and thus do much 
less in the way of fertilizing the earth, than if the same 
amount were distributed over a longer period. 

The indications of the rain, as of the other elements, would 
be more interesting, could they be compared with the average 



82 WRITINGS OF JOSEPH UEXRY. [1855- 

amount deduced from a series of observations made through 
a number of years. 

The direction of the wind, as well as the amount of cloudi- 
ness and sunshine, besides being of much importance in de- 
termining the meteorological elements of the climate of a 
country, are of interest to the farmer in comparing them 
with the other elements with which it is intimately con- 
nected, and thus deducing rules for the prognostication of the 
weather. 



-1859] WRITINGS OP JOSEPH HENRY. 83 



METEOROLOGY IN ITS CONNECTION WITH AGRICULTORB. 

PART II.— GENERAL ATMOSPHERIC CONDITIONS. 
(Agricultural Report of Commissioner of Patents, for 1866 ; pp. 455-492.) 

In the last Agricultural Report of the Patent Office I gave 
an account of the several systems of meteorology now co- 
operating in this country to advance the science, and also 
endeavored to show the importance of this branch of knowl- 
edge in its connection with agriculture. I propose in this 
Report and the subsequent ones to continue the subject, and 
to present some of the physical laws on which meteorology 
depends, the general principles at which it has arrived, and 
their application to the peculiarities of the climate of the 
United States. An exposition of this kind presented to the 
farmer through the Agricultural Report it is thought will 
serve to awaken a more lively interest in the subject, will tend 
to diffuse a knowledge of the advantages of general principles, 
and will convey information not readily accessible, and which 
in realit}^ does not elsewhere exist in the condensed form in 
which it will be here given. 

Perhaps no branch of science has given rise to more specu- 
lation or excited a greater amount of angry controversy 
than that relating to the nature and interpretation of atmos- 
pheric phenomena. The former may arise from the depend- 
ence of man for health and comfort on tlie state of the 
weather, and the latter from the limited sphere of individual 
observation to which the cultivators of this branch are gene- 
rally confined. While the astronomer, without quitting his 
observatory (if situated near the equator) can watch the 
motions of all the heavenly bodies as they present themselves 
in succession to his telescope, the meteorologist can take cog- 
nizance only of the changes which occur immediately around 
him, and hence the origin of partial views and imperfect 
generalizations. Controversies in this science, as in most 
others, may frequently however be referred to the partiality we 
entertain for the products of our own minds. Truth, as has 
been properly said, belongs to mankind in general; our 

8-2 



34 



WRITINGS OF JOSEPH HENRY. [1855- 



hypotheses belong exclusively to ourselves, and we are fre- 
quently more interested in supporting or defending these 
than in patiently and industriously pursuing the great object 
of science, namely, the discovery of what is. 

In the account of meteorology which it is proposed to give, 
the writer has no hypotheses or theories of his own to support, 
but will endeavor to confine his statements to the exposition 
of such principles as are generally recognized at the present 
day ; and if hereafter it shall be found that views have been 
presented in this paper which cannot be sustained, he will 
point out in the subsequent Reports the errors which may 
have been committed. The expounder of science, unlike the 
politician, is at liberty to change his opinions when they are 
found to be at variance with the actual condition of things. 
Indeed, in the investigation of nature, we provisionally adopt 
hypotheses as antecedent probabilities, which we seek to 
prove or disprove by subsequent observation and experi- 
ment ; and it is in this way that science is most rapidly and 
securely advanced. 

Some parts of our subject, as will be seen, are intimately 
connected with leading questions of the day ; and on this 
account it might be considered prudent to avoid allusion to 
them. But the great aim of science is the discovery of truth ; 
and the proverbial veneration entertained for it by the 
human mind is a sure indication that truth, and the whole 
truth, will always be conducive to the real progress of nations 
or individuals, and that to present it simply as a proposition 
without special application is the best means of supplanting 
error. We hold in high veneration the plan of government 
establi.shod by the wisdom of our forefathers; but we can- 
not bo blind t*) the fact that it required a peculiar theatre 
for its appli(;atioih, a wide territory of fertile soil and genial 
clinmU*, well fitted to reward the labors of the husbandman 
and to promote the health of his body and the vigorous ac- 
tivity of his mind. Next to our political organization, under 
I*rovid(jnco our prosperity has mainly been promoted by the 
ample room afForded us for expansion over the most favored 
regions of this continent. It becomes therefore important 



-1859] WRITINGS OP JOSEPH HENRY. 35 

for US to ascertain the natural limits, if there are any, to the 
arable portion of our still untenanted possessions, and to de- 
termine, if possible, what parts of it are best fitted by climate 
and soil for the future operations of the husbandman. The 
data do not exist at present for the definite solution of this 
problem; but it is one object of the systems of meteorology 
now in operation in this country to collect the facts by 
which it may be fully solved. In the. United States agri- 
culture as a science has been up to this time of compara- 
tively little importance; refined processes of cultivation are 
not required where the products of millions of acres of vir- 
gin soil can be gathered without skill and with compara- 
tively little labor. It is only when the organic power and 
material which Nature has thus stored up in the primitive 
earth have been to a greater or less extent exhausted, that 
scientific processes must be adopted in order to secure the 
continued production of ample harvests. The time is at 
hand when scientific agriculture can no longer be neglected 
by us; for however large our domain really is, and however 
inexhaustible it may have been represented to be, a sober 
deduction from the facts which have accumulated during 
the last few years will show that we are nearer the confines 
of the healthy expansion of our agricultural operations over 
new ground than those who have not paid careful attention 
to the subject could readily imagine. We think it will be 
found a wiser policy to develop more fully the agricultural 
resources of the States and Territories bordering on the Mis- 
sissippi, than to attempt the further invasion of the sterile 
waste that lies beyond. 

The laws of nature are all simple and readily compre- 
hended by a mind of ordinary capacity, when separately an- 
nounced; but when the conditions under which they operate 
are varied, and a number of forces are called into action, the 
resulting phenomena frequently become so complex that 
their investigation transcends not only the ordinary logic of 
the most gifted mind, but even the more powerful analysis of 
the mathematician. It has been well said by Professor Ben- 
jamin Peirce, of Cambridge, that had the lot of man been cast 



36 WRITINGS OF JOSEPH HENRY. [1S55- 

upon one of the outer planets of our system, the phenomena 
of the motions of the heavenly bodies, as viewed from that 
point, would have been so complex and apparently irregular, 
that our present state of civilization (resting as it does on the 
principles of science beginning with astronomy, the most 
perfect) would not have existed : man would never have ar- 
rived at the definite idea and the conclusive evidence of 
the universality of causation. In other words, that amid 
all the apparently confused and accidental occurrences which 
we observe, a few simple laws (constantly diminishing in 
number as our views become more extended) govern all 
events, whether they be those which we refer to order and 
succession, or those which in our ignorance we ascribe to 
to chance. Astronomy is the most perfect of all the sciences, 
not only because it has been longer studied, but more espec- 
ially because it is the simplest exhibition of the laws of force 
and motion; and yet even in this science where all the data 
are furnished, the introduction of a few conditions renders a 
problem too complex for direct solution. For example, to 
determine the path described and the time of revolution of 
a single planet round the central body by the application of 
the laws of motion and gravitation is a simple problem, 
which was solved at an early period in the history of astron- 
omy. When however a third body was introduced, such for 
example as the moon, in addition to the earth and sun, the 
problem baffled for a long time the skill of the first mathe- 
maticians of the age; and even yet a direct d priori solution 
of all the results which will be produced by the mutual action 
of a series of planets revolving round the sun has not been 
efiected, and recourse is had to indirect methods of approx- 
imation. Had man confined his observations to the complex 
and multiform changes of the weather, the probability of his 
ever arriving at a definite law would be far less than even in 
the before mentioned case of astronomy ; for, though we are 
assured that the motion of every atom of air is governed by 
the same laws which direct the heavenly bodies, yet the 
amount of perturbation and reciprocal action presented in 
the case of myriads of atoms renders the probability of a com- 



-1859] WRITINGS OF JOSEPH HENRY. 37 

plete solution of the problem of the currents of the atmos- 
phere, even with the greatest possible extension of human 
science, extremely doubtful. We must therefore be content 
with approximations deduced from general principles com- 
bined with the results of extended, precise, and definite ob- 
servation. 

The history of meteorology illustrates the fact, that what 
may be termed popular observations and experience, without 
scientific direction, seldom lead to important rules. The 
uneducated sailor of to-day, after three thousand years of ex- 
perience, firmly believes that he can invoke the winds and 
entice them from the caves of jEoIus by a whistle. Most of 
the aphorisms in reference to the changes of the weather, 
though of venerable antiquity, merely relate to the greater or 
less degree of moisture in the atmosphere. They declare 
what has happened, that a change has already taken place 
in the air, but give no certain indication of what is to occur. 
In order therefore to the successful study of meteorology, the 
results of systematic observations are to be compared with the 
deductions from well established principles of science, and 
the converse; or in other words, deduction and observation 
should constantly go hand in hand, the former directing the 
latter, and the latter correcting the conclusions of the former. 

In meteorology, as in all other branches of science, the im- 
portant rule adopted by Newton should never be neglected, 
namely: "No more causes are to be admitted for the explan- 
ation of any phenomenon, or class of phenomena, than are 
true and suflBcient." Though a general principle which is 
in strict accordance with the established laws of force and 
motion cannot be immediately applied to the explanation of 
an isolated class of phenomena, it is not, on that account, to 
be set aside for some new and unknown agent. We must 
look to further investigations for the light which shall 
enable us to perceive the connection. The lindulatory theory 
of light connects so many facts, and has enabled the scientist 
to predict so many others which were previously unknown, 
that though a few outstanding phenomena may still exist 
they do not militate against our convictions of the truth of 



38 WRITINGS O^ JOSEPH HENRY. [1855- 

the generalization which this theory so admirably expresses; 
and we may safely attribute the apparent want of agreement 
to our ignorance of some essential condition of the phenom- 
ena in question, or to some error in the logical deduction 
from our principles. The history of science abounds in ap- 
parent Q^cceptions to general rules which when better un- 
derstood become additional evidences in support of the gen- 
eral principle. The foregoing remarks will not be thought 
inapplicable on the present occasion by those who have 
studied the history of the progress of meteorology. 

One of the most important general truths at which science 
has arrived by a wide and cautious induction, and which is 
the foundation of meteorology, is that nearly all the changes 
which now take place at the surface of the earth are due to 
the action of the sun. The forces which pertain to the earth 
itself — ^such as gravity, chemical affinity, cohesion, electricity, 
magnetism, &c. — are forces of quiescenje; they tend to bring 
matter to a state of rest at the surface of the globe, from 
which it is only again disturbed by the solar emanation. 
All the elementary substances which constitute the surface 
of our planet, with the exception of the organic matter, have 
long since gone into a state of permanent combination. The 
rocks and various strata are principally composed of burnt 
metals. The whole globe is an immense slag, analogous to 
that drawn from the smelting furnace, surrounded by a 
liquid and an aerial envelope ; the former in a state of ulti- 
mate chemical combination, and the active principle of the 
latter — the oxygen — finding nothing to combine with, except 
what has been released from a former combination by the 
action of the sun. If therefore the solar impulses were sus- 
pended, all motion on the surface of the planet would cease: 
the wind would gradually die away ; the currents of the 
ocean would slacken their pace, and finally come to rest ; 
and stillness, silence, and death would hold universal reign. 
We cannot however at present pursue this thought, but 
must confine our remarks to the effects of those impulses of 
the sun denominated heat in their connection with meteo- 
rology. 



-1859] WRITINGS OP JOSEPH UENRY. 39 

All the phenomena referable to heat from the sun acting 
under varying conditions will now (so far as they affect the 
climate of the United States,) be considered under two heads: 

1. The effects of varying astronomical conditions, irres- 
pective of atmospheric and other influences. 

2. The effect of all conditions, other than astronomical, 
such as the influence of the air, the ocean, the land, &c. 

J. ReauUs of Astronomical Conditions. 

The earth, in its annual revolution in its orbit round the 
sun, does not describe a perfect circle, but an ellipse, of which 
the sun occupies one of the foci ; and hence we are nearer 
at one season of the year to this central luminary than at 
another. It is well established by mathematical investi- 
gation from astronomical data, that at the present histori- 
cal period, the earth as a whole receives the greatest amount 
of heat during any*one day in the year on the first of Jan- 
uary, and the least amount on the 4th of July. The 
variation in the distance of the sun produces no effect on 
the different seasons ; since the rapidity of motion or the 
less duration of proximity to the sun, just compensates for 
the greater intensity of the rays due to the nearer approach. 
Were it not for this, the eccentricity of the orbit would 
materially influence the heat of the seasons, since the fluctua- 
tion in the heating power of the sun's rays on this account 
amounts to one-fifteenth of the whole; and it does in reality 
increase the diurnal intensity for a few days in January, 
as is shown from the ardor of the sun's rays under a clear 
sky at noon in the southern hemisphere. One-fifteenth, 
says Sir John Herschel, is too considerable a fraction of the 
whole intensity of sunshine, not to aggravate in a serious 
degree the sufferings of those who are exposed to it without 
shelter, in the thirsty deserts of the south. The accounts 
of what is endured in the interior of Australia at this season, 
for instance, are of the most frightful kind, and seem far 
to excel what liave ever been experienced by travellers in 
any part of the northern hemisphere. 

Another astronomical deduction is that the point of the 



40 WRITINGS OF JOSEPH HENRY. [185S- 

earth's orbit which approaches nearest the sun is constantly 
changing its place, and in time the order will be reversed; 
the greatest amount of heat from this cause will be on some 
day in July, and the least in January. But this change is 
so slow, that no appreciable eflFect has been produced during 
the historic period. A slight variation also takes place in 
the distance of the earth and sun when nearest to each other; 
but this also is confined to such narrow limits, that it is 
entirely insuflScient to account for the changes undergone 
in the earth's temperature, as indicated by fossil plants and 
animals, and cannot, on account of its slowness, have had 
any appreciable effect upon the temperature of any part of 
the earth since the first records of civilized man. If there- 
fore it be true, as some suppose, that the seasons have 
changed in different parts of the earth within the memory 
of man, the effect must be due to other than to astronomi- 
cal causes. 

The earth is approximately a sphere, and consequently, 
the sun's rays strike it obliquely at all places, except those 
over which it is precisely vertical. The amount of variation 
on this account can readily be calculated ; the sun's beam 
may be considered as a force, and resolved into two parts, 
one of which is parallel to the surface of the earth, and the 
other perpendicular to it, the latter alone producing the 
result. The intensity of the sun's beam will be the greatest 
at the equator, and will gradually diminish to the poles. It 
is true the sun does not continually remain vertical at the 
equator, but the average result in the course of the year, is 
nearly the same as if this were the case ; since the greater 
amount of heat received while he is at the north just com- 
pensates for the less while at the south. The average tem- 
perature of any given place, in consideration of the obliquity 
of the rays which the earth would receive if uninfluenced by 
other conditions, can be obtained by multiplying its equa- 
torial temperature into the radius of its parallel of latitude; 
or (in more technical language) into the cosine of the latitude. 

From this formula, which we owe to Sir David Brewster, 
we have calculated the following table, which exhibits the 
astronomical and observed temperatures of the valley of the 



-1859] 



WRITINGS OF JOSEPH HENRY. 



41 



Mississippi, along a line passing through the city of New 
Orleans: 



Lat. 


Astron. mean 


Observed temp. 


Differ- 


temp. 


reduced. 


ence. 


25« 


74-82 


74-60 


+ 0-18 


80« 


71-01 


69-00 


— 2-01 


85« 


6717 


62-00 


— 6-17 


40® 


62-81 


6300 


— 9-81 


46® 


67-98 


44-60 


—13-48 


W> 


62-70 


87-00 


—16-70 



The temperature of the equator is assumed to be 82*^. 
The first column gives the latitude, the second the astro- 
nomical mean temperature, the third the observed temper- 
ature reduced to the level of the sea, as taken from the 
accompanying isothermal chart,* and the fourth column the 
diflFerence between the last two. It will be seen that the 
difference between the calculated and the observed temper- 
ature in the lower latitudes is quite small; but as the lati- 
tude increases, the deviation becomes very great. This 
difference is due to other than astronomical causes, and by 
eliminating the latter we narrow the field of research. 

Empirical formulas of much nearer approximation to the 
truth in high latitudes have been proposed, which will be 
noticed hereafter, our object at present being only to exhibit 
the diflFerence between the astronomical results and those 
derived from actual observation. 

Let us next consider the changes of temperature in diflfer- 
ent parts of the day and in diflPerent seasons of the year, 
produced by the varying obliquity of the sun's rays. If we 
assume a given length of sun-beam as the representative of 
the force, and then resolve this into two, — one perpendicular, 
the other parallel to the horizon, — the sum of all the perpen- 
dicular lines, from the rising to the settmg of the sun on any 
day, will represent the whole intensity of the heat on a given 
place during that day; and in this way may be calculated 
the relative amount of heat received on diflferent latitudes 
at diflferent seasons of the year. From this estimate we shall 
find that the amount of heat received from the sun during 
a given day in summer, say the 16th day of June, at dif- 

* [See Map, at page 72.] 



42 



WRITINGS OF JOSEPH HENRY. 



[185S- 



ferent northern latitudes, is greater than that which falls 
upon the equator during the same time. This is exhibited 
in the following table, from the paper of L. W. Meech on the 
sun's intensity, in the 9th volume of the Smithsonian C!on- 
tributions, [page 18] : 

The sun^a diurnal inUnsity at every ten degrees of latitude in the northern 

Jiemxephere, 



1853. 



Jan. 1 :. 

Jan. 16 

Jan. 31 

Feb. 16 

Mar. 2 

Mar. 17 

April 1 

April 16 

May 1 

May 16 

May 31 

June 16 

July 1 

July 16 

July 81 

Aug. 15 

Aug. 30 

Sept. 14 

Sept. 29 

Oct. 14 

Oct. 29 

Nov. 13 

Nov. 28 

Dec. 13 



Lat. 



771 
781 
79-6 
810 
81-6 
820 

80-8 

790 
76-9 
74-7 

73 
720 
720 
730 

74-7 
76-7 

78-6 
79-8 

80-5 
80-7 
79-9 
78-8 
77-6 
76-9 



Lat. 
10*>. 



67-2 
68-9 
71-7 
74-7 
78 
80-2 

81-4 

81-7 
81-5 
80-8 

801 
79-6 
79-6 
79-8 

80-4 
80-8 

80-7 
79-8 

78-4 
76-4 
73-5 
70-7 
68-3 
66-9 



Lat. 
20<». 



55-8 
68-2 
61-9 
66-6 
71-3 
76 

79-6 

820 
83-7 
84-7 

851 
86-2 
850 
84-7 

83-9 
82-7 

80-6 
77-5 

73-8 
69-7 
650 
60-8 
57-3 
55-4 



Lat. 
30O. 






42*8 
45-8 
49-7 
55-6 
62-9 
69-6 

75-3 

79-6 
83-6 
86-7 

87-8 
88-4 
88-5 
87-5 

851 
82-4 

77-7 
72-6 

67 
610 
54-6 
49-8 
45-3 
430 



Lat. 
40*>. 



801 
32-7 
38-6 
451 
52-7 
611 

68-9 

761 
80-8 
85-7 

88-9 
901 
90-4 
87-6 



84-5 
79-8 

721 
65 6 



67-8 
60-2 
42-5 
371 
31-8 
30-3 



Lat. 
60O. 



16-6 
19-3 
250 
31-9 
411 
50-2 

60-2 

68-6 
771 
83-3 

87-8 
89-9 
89-5 
86-5 

81-6 
74-7 

65-5 
58-8 

47 
38-2 
301 
23-8 
18-9 
16-3 



Lat. 
60^. 



51 
7-2 
11-9 
190 
27-9 
371 

49-9 

611 
70-9 
79-7 

85-7 
88-8 
88-4 
841 

77-3 
68-2 

57-3 
46-9 

36-2 
25-7 
17-5 
110 
6-8 
4-9 



Lat. 
70<». 



1-4 

6-4 

14*5 

25-5 

880 

51-4 
64-6 
76-8 

86-8 
91-7 
90-8 
84-8 

73-4 
60-9 

47-7 
34-5 

22-6 

12-6 

5-2 

0-9 



Lat. 
80«. 



21 
11-6 

25-6 

44 
643 
80-3 

910 
961 
951 

88-3 

76-2 
59-2 

38-8 
21-9 

90 
10 



Lat. 



20-6 

44*6 
65-8 
81-6 

92-4 
97-6 
96-6 
89-7 

77-4 
60-1 

38-9 
14-7 



On the fifteenth of June the sun is more than 23 degrees 
north of the equator, and therefore it might be readily in- 
ferred that the intensity of heat should be greater at this 
latitude than at the equator ; but that it should continue to 
increase beyond this even to the pole, as indicated by the 
table, may not at first sight seem so clear. It will how- 
ever be understood, when it is recollected that the table in- 
dicates the amount of heat received during the whole day ; 



-1859] WRITINGS OP JOSEPH HENRY. 43. 

and though in a more northern latitude the obliquity of the 
ray is greater, and on this account the intensity should be 
less, yet the longer duration of the day is more than suflB- 
cient to compensate this effect, and to produce the result ex- 
hibited. This is an important fact, in comparing the agri- 
cultural capacity of different latitudes ; for though there is 
absolutely more heat at the latitude of New Orleans during 
the year than at Madison, in Wisconsin, yet there is more heat 
received at the latter place during the three months of mid- 
summer than in the same time at the former place. An 
analogous but contrary result is exhibited in regard to the 
cold of winters, as will be seen by the table. It is from 
this principle that as we advance toward the equator, the 
extreme variations of the season become less and less. It 
is important to remark in this place that the foregoing 
tables exhibit the amount of heat actually falling upon the 
earth during the day as unmodified by any extraneous 
causes. They do not however exhibit the hottest portion of 
the season. This will depend upon another condition, which 
may be properly explained in this connection, though it is 
not classed under the astronomical causes. It is a well es- 
tablished principle that all bodies are radiating heat even 
while they are receiving it. If the amount received in a 
definite time is greater than that given off, the temperature 
will increase; on the contrary, if the amount given off is 
greater than that received, the temperature will diminish. 
The earth is constantly radiating heat into space, but only 
receiving it from the sun during the day. As the sun is de- 
clining towards the south, the daily amount received at 
length becomes less than that given off in the night, and 
hence the temperature begins to fall ; and this diminution 
will continue until the two quantities again become equal, 
which will not be at the point where the greatest amount of 
heat is given off. On the twenty-first of June, in northern 
latitudes, the earth is receiving the greatest amount of heat, 
and hence it is becoming heated up most rapidly at this 
time. On the twenty-second it receives a less amount of heat, 
but the heating continues, since the gain is still greater than 
the loss; and this goes on until about the 25th of July, or 



44 



WRinXGS OF 



later, after which the radiation daring the day and night 
together exceeds the amount received from the sun doring 
the day, when the temperature begins to decline. The 
action is a little complicated, on account of the fact that the 
radiation increases with the temperature. A similar result 
is produced in the heating of the day, as will be seen from 
the following table of observations taken at every hour of 
the twenty-four, at Girard College, imder the direction of 
Professor Bache : 

MEAX DimXAL TA»IATI03f OF THE TKMFEEATCHE OF THE Aim AT 

PHIULDELPHIA. 

Computed frrtm obsrrrai'u*Kf in 1S42. as%d /rum Julw 1, 184S, to July 1, 184&. 



1 

A. M . 


2 1 3 

A.M. A.M. 


4 5 6 7 8 

A.M. A.M. A.M. A.M. A.M. 


9 10 11 

A.M. A.M. A.M. 


12 
xoox. 


i8-2 


1 

47-8 i 47-3 

1 1 


40 8 4»>-6 470 481 oO I 

; 1 1 


521 541 ' 55-7 

1 1 


56-8 



Mlnimufn. 



1 

p. M. 


2 

P.M. 


3 

p. M. 


4 

p. M. 


5 6*78 9 10 11 

p. M. p. M- p. M. P. M. P. M. P. M. P. M. 

1 1 


12 

' KIOHT. 


57-9 


58-6 


58-9 


58-7 


57 7 >5-0 54 1 52 5 51-0150-2 494 

; 1 1 i 


48-7 



Maximum. 

The result in the above table is somewhat aflFected by the 
greater humidity of the atmosphere towards morning, which 
prevents a greater radiation and fall of temperature, even 
after the rising of the sun. 

//. — Results of other than Astronomical Conditions, 

The deductions tliat have thus far been given are from 
established astronomical data; and unless some error has 
been committed in the statement, their correctness cannot 
be doubted by any person properly educated in the line of 
physical science. The effects produced by the air, the water, 
and the land, are however of a much more complicated 
character, and like the problem of the mutual action of all 
the planets on each other, have never yet been submitted to 



-1859] WRITINGS OP JOSEPH HENRY. 45 

a saccessful mathematical analysis. In the investigation of 
a phenomenon, it is not enough that we explain how it is 
produced ; besides this, positive science requires that the ex- 
planation be true in measure as well as in mode, and indeed 
it is only when we can predict, the exact amount of an effect, 
the principle being known and certain data given, that a 
phenomenon can be said to be perfectly analyzed. We have 
seen in the preceding paragraphs that the meteorological 
phenomena produced by astronomical causes admit of rela- 
tive numerical expression ; but in what follows we are obliged 
to content ourselves with the explanation in mode, and to 
refer to direct experiment and observation for the amount 
of the eflFect in measure. It is in this part of meteorology 
that so much uncertainty prevails, and in reference to which 
so much discussion, even of an excited character, has arisen. 
As was said before, the writer has no hypothesis of his own 
to advance and will therefore confine himself to a statement, 
and in some cases a brief examination, of such hypotheses 
relative to the eflFects of the atmosphere, the ocean, &c., in 
modifying climate as have been suggested, and which appear 
to be in accordance with established principles. 

Effects of tlie Atmosphere in a Statical Condition. — ^Were it 
not for the aerial envelope which surrounds our earth, all 
parts of its surface would probably become as cold at niglit, 
by radiation into space, as the polar regions are during 
the six months' absence of the sun. The mode in which 
the atmosphere retains tlie heat and increases the tem- 
l)erature of the earth's surface may be illustrated by an 
experiment originally made by Saussure. This physicist 
lined a cubical wooden box with blackened cork, and, 
after placing within it a thermometer, closely covered it with 
a top of two panes of glass, separated from each other by 
a thin stratum of air. When this box was exposed to the 
perpendicular rays of the sun, the thermometer indicated a 
temperature within the box above that of boiling water. 
The same experiment was repeated at the Cape of Good 
Hope, by Sir John Herschel, with a similar result, which was 
however rendered more impressive by employing the heat 
thus accumulated in cooking the viands of a festive dinner. 



46 WRITINGS OP JOSEPH HENRY. [185S- 

The explanatioQ of the result thus produced is not difficult 
when we understand that a body heated to different degrees 
of intensity, gives off rays of different quality. Thus if an 
iron ball be suspended in free space and heated to the tem- 
perature of boiling water it emits rays of dark heat, of little 
penetrating power, which are entirely intercepted by glass. 
As the body is heated to a higher degree, the penetrating 
power of the rays increases; and finally when the tempera- 
ture of the ball reaches that of a glowing or white heat, it 
emits rays which readily penetrate glass and other trans- 
parent substances. The heat which comes from the sun 
consists principally of rays of high intensity and great pene- 
trating power. They readi ly pass through glass, are absorbed 
by the blackened surface of the cork, and as this substance 
is a bad conductor of heat, its temperature is soon elevated, 
and it in turn radiates heat ; but the rays which it gives off 
are of a different character from those which it receives. 
They are non-luminous, and have little penetrating power; 
they cannot pass through the glass, are retained within the 
box, and thus give rise to the accumulation of heat. The 
limit of the increase of temperature will be obtained when 
the radiation from the cork is of such an intensity that it 
can pass through the glass, and the cooling from this source 
becomes just equal to the heating from the sun. The atmos- 
phere surrounding the earth produces a similar effect. It 
transmits the rays of the sun which heat the earth beneath ; 
but this in turn emits rays which do not readily penetrate 
the air, thus effecting an accumulation of heat at the surface. 
The resistance of the transmission of heat of low intensity 
depends upon the quantity of vapor contained in the atmos- 
phere, and perhaps also on the density of the air. The 
radiation of the earth therefore differs very much on different 
nights and in different localities. In very dry places, as for 
example in the African deserts and our own western plains, 
the heat of the day is excessive, and the night commen- 
surably cool. Colonel Emory states in his Report of the 
Mexican Boundary Survey that in some cases on the arid 
plains there was a difference of 60° between the temperature 
of the day and that of the night. Indeed the air in this re- 



-1859] 



WRITINGS OP JOSEPH HENRY. 



47 



gion is so permeable to heat, even of low intensities, that a 
very remarkable difiFerence was observed on some occasions 
when the camp-ground was chosen in a gorge between two 
steep hills. The inter-radiation between the hills prevented 
in a measure the usual diminution of temperature, and the 
thermometer in such a position stood several degrees higher 
than on the open plain. 

We shall next briefly consider the mechanical constitu- 
tion of the atmosphere. The aerial ocean which surrounds 
the earth consists of atoms of matter self-repellant, which in 
proportion as the interior pressure is lessened, constantly tend 
to separate from each other and produce an enlargement or 
expansion of the whole mass. When the pressure is in- 
creased the mass sinks into a less volume, the atoms are 
brought nearer together, the force of repulsion is increased 
with the diminution of distance between the atoms, and a 
new equilibrium is attained. From this constitution of the 
air it immediately follows that the density of the atmosphere 
is greater near the surface of the earth than that at a higher 
altitude, since the lower stratum bears the weight of all those 
which are above it. The diminution in weight of equal 
bulks of air as we ascend is in a greater ratio'than the height, 
since it diminishes on two accounts: first, because as wo 
ascend in the air the number of strata pressing on us is less; 
and secondly, each succeeding stratum is lighter. From the 
law of this diminution of density a table may be formed of 
the pressure of the atmosphere at various heights, of which 
the following is an example: 



Density of the air at increasing altitudes. 


Miles above 
the sea. 


Bulk of equal 
weight of air. 


Density. 


Height of 
barometer. 





1 


1 


3000 


3-4 


2 


} 


1600 


6-8 


4 


} 


7-50 


10-2 


8 


3-75 


18-6 


16 


A 


1-87 . 


170 


32 


5a 


0-93 



48 WBITINQS OF JOSEPH HENRT. [1855- 

From this table it appears that one-half of the whole 
atmosphere is found within the upward limit of 3{ miles, 
and one-third of the whole quantity beneath the average 
height of the Rocky Mountains: this fact has an important 
bearing on the influence of mountain ranges in modifying 
the direction of the winds. 

The question occurs at this place, Why does the air grow 
colder as we ascend? The answer is that a pound of air, 
at all distances above the earth contains at least an equal 
amount of heat with the same weight taken at the surface, 
and that as the pressure is removed this air is expanded in 
bulk; consequently the heat is difiFused through a greater 
amount of space, and hence the reduction of its intensity or 
temperature. To illustrate this, take a large ball of sponge 
and squeeze it into one quarter of the space which it natur- 
ally occupies; in this condition dip it into water, it will 
imbibe a certain quantity of the liquid, and when drawn out 
will be dripping wet; now let it expand to its natural dimen- 
sions, the water will be distributed through a large amount 
of space, and the sponge itself will appear comparatively dry. 
Squeeze it again into its former condensed state, and it will 
appear wet; suffer it again to expand, and the apparent 
dryness will be resumed. In a like manner we suppose that 
while the quantity of heat is the same, its intensity is in- 
creased by condensation into a smaller space and diminished 
by the convei'se process. In the foregoing illustration the 
amount of water contained in the sponge represents the 
amount of heat in the air, and the degree of wetness pro- 
duced by condensation the intensity of the temperature 
exhibited in diminishing the bulk of air. 

It follows from this that the blowing of a current of air 
over a high mountain, provided it descends again into the 
plain, does not necessarily diminish its temperature. When 
it arrives at the top of the mountain, it will become as cold 
as the circumambient air, not because it has lost any of its 
heat, but because that which it contained is now distributed 
through a greater space; when it descends again to the plain, 
it will suffer a corresponding diminution of bulk, on account 



-1859] WBITINQS OP JOSEPH HENRY. 49 

of the increased pressure, and with this the original tempera- 
ture will be restored. 

This principle, as we shall see hereafter, is of great im- 
portance in the study of the peculiarity of the temperature 
of the western portion of the territory of the United States. 
We have said that every pound of air, from the bottom of 
the aerial ocean to its surface above, contains at least an 
equal quantity of heat; and this was the inference of Dal- 
ton'. From the investigations of Poisson and others it ap- 
pears that the absolute quantity of heat, pound for pound, 
slightly increases rather than diminishes as we ascend; and 
this seems necessary to the stability of the equilibrium of 
the atmosphere as a whole. If the amount of heat were 
greater in the lower strata than in the upper, the equilibrium 
would be unstable, and an inversion would tend constantly 
to take place. An equal quantity of heat, (pound for pound,) 
as we ascend, would produce an indifiFerent equilibrium, 
while an increased amount in the order of ascent, would 
produce a stable condition of the atmosphere, such as that 
which really exists. The question however has not yet been 
fully settled, although it is an important one having a bear- 
ing on the explanation of many meteorological phenomena. 
Another question of much interest is the exact law of 
diminution of temperature as we ascend into the air. Were 
this actually known, we could reduce to the same level all 
the observations which are made in a country; and thus, in 
addition to the astronomical effects, we could eliminate those 
due to altitude, and present the remainder as results which 
are due to the other conditions producing the peculiarities 
of climate. In order however to apply the law with pre- 
cision in this way, it is desirable that it should be deter- 
mined from observations made by ascents in balloons or at 
. points of difiFerent heights on isolated mountain peaks. 
Relative observations made for this purpose on the top and 
at the base of mountain systems of considerable width and 
extent will probably give results involving the influence ot 
the mountain surface itself, which in turn would be some- 
what affected by the direction of the prevailing wind and 

4-2 



•60 WRITINGS OF JOSEPH HENRY. [1855- 

other causes. The progress of meteorology will call tor an 
increased number of observations of the proper diaracter, 
and for the repetition of the experiments vrith balloons, in 
different parts of the earth. 

Celestial space, in which our sun and the earth and other 
planets of our system are placed, is known, from difiFerent 
considerations, to have a temperature of its own, which is 
supposed to be the result of the inter-radiation of all the suns 
and planets which exist in every part of the visible universe. 
The temperature of this space is estimated to be about — 60°. 
This fact being allowed, it will follow (since the heat at the 
top of the air remains constant) that the rate of decrease of 
temperature as we ascend will be diminished with the 
decrease of temperature at the surface of the earth, and also 
that the rate of decrease will follow a slightly diminishing 
ratio. At all accessible elevations in the atmosphere how- 
ever it may be considered as almost constant. In some 
cases the rate of diminution is interfered with by abnormal 
variations of temperature ; for example, as we ascend into the 
region of the clouds, the latent heat evolved in the conden- 
sation of the vapor produces a loc^l heat in the atmosphere 
beyond the natural temperature. In temperate latitudes it is 
usual to allow 300 feet of elevation for the reduction of tem- 
perature one degree of Fahrenheit's scale. This quantity 
was deduced from thirty-eight observations collected by 
Ramond. Boussingault found, from observation in the tropics, 
the diminution at 335 feet. Col. Sykes, from mountain ob- 
servations in India, the diminution at 332 feet. Saussure 
ascertained the mean value in the Alps to be 271 feet. Gay 
Lussac's celebrated voyage gave 335 feet. And the result 
of several series of observations with the balloon by Mr. 
Welch, under the direction of the British Association, omit- 
ting the points unduly heated by the condensation of vapor, 
was about 320 feet. In the construction of the isothermal 
chart * we have adopted 333 feet, or three degrees to one 
thousand feet, as the rate of diminution, and find in com- 
paring the temperature of different places of varying heights 

*[See Map, at page 72.] 



-1859] WRITINGS OP JOSEPH HENRY. 51 

which have been reduced by it, that they afiFord very satis- 
factory corresponding results. We propose to give a fuller 
discussion of this part of the subject in another report. 

Motions of the AtTnosphere, — ^The repulsion of the atoms of 
the air is not only increased by a diminution of distance 
from being pressed closer together, but also by an addition 
of heat. From the latest and most reliable experiments on 
this point it is found that the pressure being the same, air 
expands ^Jr part of its bulk at the freezing point for each 
degree of Fahenheit's scale. Heated air therefore becomes 
specifically lighter, and tends constantly to ascend, being 
pressed upwards by the heavier circumambient fluid. The 
effect thus produced upon the air by the impulses from the 
sun is the great motive power which gives rise to all the 
currents of the atmosphere, from the gentle zephyr which 
slightly ripples the surface of the tranquil lake to the raging 
hurricane which overwhelms whole fleets, or destroys in a 
moment the hopes of the husbandman for an entire season. 
This fact is so well established by science that it is unnecessary 
to seek for any other primum mobile for the great system of 
constant agitation to which the aerial ocean is subjected. 

Allowing the temperature of the equator, on an average, 
to be 82° F., that of the pole zero, and of the top of the air, or 
in other words, of celestial space, to be — 60°, and estimating 
the height of the atmosphere at 50 miles, it will follow from 
the law of expansion by heat, that the excess of elevation of 
the air at the equator will be upwards of four miles above 
that of the pole. Although this is not intended to present 
the exact amount of the aerostatic pressure, yet it will serve 
to show the great motive power constantly maintained by 
the influence of the solar radiation. In order to simplify 
the conception of the motions which result from this dis- 
turbing power, let us in the first place, suppose the earth to 
be at rest, and its whole surface of a uniform character, con- 
sisting, for example, of water. It is obvious from well estab- 
lished hydrostatic principles, that the air expanded as we 
have stated at the equator, would flow over at the top and 
descend, as it were, along an inclined plane towards the 



62 WRITINGS OF JOSEPH HENRY. [1855- 

poles, would sink to the eartli, flow back to the equator 
beloWy and would again be elevated in an ascending cur- 
rent; and thus a perpetual circulation from either polo to 
the equator, and from the equator back towards the poles, 
along the several meridians of the globe, would be the con- 
tinuous result. It is further evident that since the meridians 
of the earth converge, and the space between them constantly 
becomes less, all the air that rose at the equator would not 
flow along the upper surface entirely to the poles, but the 
greater portion would proceed north and south no further 
than the 30® of latitude; for the surface of the earth con- 
tained between the parallel of this degree and the equator 
is equal to that of half of the whole hemisphere. Portions 
however in the northern hemisphere, for example, would 
flow on to descend at different points further north ; and of 
these some would probably reach the pole, there sink to the 
surface of the earth, and from that point diverge in all direc- 
tions in the form of a northerly wind. Between the two 
ascending currents near the equator would be a region of 
calms or variable winds, influenced by local causes. The 
currents which flow over towards the poles would descend 
with the greatest velocity at the coldest point; because there 
the air would be most dense, or would have the greatest spe- 
cific gravity. 

According to the view here presented, a section of the 
atmosphere made by cutting through a meridian from pole 
to pole, perpendicular to the horizon, would exhibit two 
great systems of circulation ; one from the north and another 
from the south to the equator below, rising at the latter 
place, and pouring over on either side to return again by 
longer or shorter circuits to the place whence they started. 
Such would be the simple circulation of the aerial ocean if 
no perturbing influences existed, and the whole science of 
meteorology would be one of comparatively great simplicity. 
But this is far from being the case. A number of modifying 
conditions must be introduced, which tend greatly to per- 
plex the anticipation of results. First, the earth is not at 
rest, but in rapid motion on its axis from west to east 



-1859] WRITINGS OP JOSEPH HENRY. 53 

Every particle therefore of the current of air as it flows 
towards the equator in the northern hemisphere would par- 
take of the motion of the place at which it started, and in 
its progress southward it would reach in succession latitudes 
moving more rapidly than itself. It would thus as it were ^ 
continually fall behind, and appear to describe on the sur- 
face of the earth a slightly curvilinear course towards the 
west. A similar result would be produced on the south side 
of the equator; and hence we have the first conception of 
the cause of the great systems of currents denominated the 
"trade winds," blowing constantly within the parallel of 30° 
from the northeast in the northern hemisphere, and from 
the southeast in the southern, towards the belt of the greatest 
rarefaction. 

The motion however will require further consideration. 
The particles of air approaching the equator will not ascend 
in a perpendicular direction, as was first supposed, but as 
they rise will continually advance towards the west along an 
ascending plane, and will continue for a time their westerly 
motion in the northern hemisphere after they have com- 
menced their return towards the north. They will how- 
ever as they advance northward, arrive at parts of the 
earth moving so much less rapidly than themselves, that 
they will gradually curve around towards the east, and 
finally descend to the earth, to become again a part of the 
surface trade wind from the northeast. The particles will 
tend to move westward as they ascend: first, on account 
of their momentum in that direction; and secondly, be- 
cause, as they reach a higher elevation, they will have less 
easterly velocity than the earth beneath. They will also be 
affected by another force, as has lately been shown by Mr. 
W. Ferrel, due to the increase of gravity which a particle of 
matter experiences in travelling in a direction opposite to 
that of the rotation of the earth. The last mentioned cause 
of deflection will operate also in a contrary direction on the 
atoms when they assume an easterly course. 

The result of the complex conditions under which the 
motive power acts in such a case would be to produce a sys- 



64 WRITINGS OP JOSEPH HENRY. [1855- 

torn of circuits inclined to the west; the eastern portion of 
which would be at the surface, and the western at different 
elevations even to the top of the atmosphere. To give 
definiteness to the conception, let us suppose a series of 
books to be placed side by side on edge, pointing to the 
north ; these books would represent the planes in which the 
currents of the air would circulate in the northern hemis- 
phere, were the earth at rest; but if the earth is supposed 
to be in motion, then the books must be inclined to the 
west, so as to make an acute angle with the horizon, and 
overlap each other like the inclined strata in a geological 
model. If on each leaf of each book a circuit of arrows be 
drawn, then will the assemblage of these represent the paths 
of the difiFerent particles of the atmosphere. The currents of 
air however would not be in perfect planes, but in surfaces 
which could be represented by bending the leaves to suit 
the curvature of the earth. In this manner would be ex- 
hibited the general motion of the wind, which has been de- 
termined by actual observation. 

The greater portion of the circulation would descend to 
the earth within 30 degrees of the equator^ giving rise to the 
trade winds; a portion would flow further north, and pro- 
duce the southwest winds; another portion would extend 
still further northward, descend towards the earth as a north- 
west wind, and so on. The air which descends in the region 
of the pole would not flow directly southward, but, on ac- 
count of the rotation of the earth, would turn towards the 
west and become a northeasterly current. At first sight it 
might appear that the north wind which descends from the 
polar regions would continue its course along the surface 
until it joined the trade winds wuthin the tropics; but this 
could not be the case, on account of the much greater 
western velocity this wind would require from the rapidly 
increasing rotary motion as we leave the pole. There would 
therefore be three distinct belts in each hemisphere, namely, 
the belt of easterly winds within the tropics, the belt of 
westerly in the temperate zone, and the belt of northwesterly 
at the north. The existence of these belts has been clearly 



-1859] WRITINGS OF JOSEPH HENRY. 55 

made out by Professor James H. Coffin in calculating the re- 
sultant of all the winds of the northern hemisphere, after hav- 
ing eliminated the effects of extraneous action, and thereby 
exhibiting the residue as the result produced by the gen- 
eral circulation. 

Another condition however must be introduced. These 
belts would not be stationary, but would move laterally to- 
wards the south or the north, according to the varying posi- 
tions of the sun at different seasons of the year. Their 
breadth would also vary ; because they would be crowded 
into a smaller space towards the pole in the wintor, and ex- 
panded into a wider gpace in the summer. 

To trace with precision the path which would be described 
by a particle of air in its circuit, while under these vary- 
ing perturbing influences, transcends the power of un- 
aided logic, and could only be accomplished (if at all) by 
means of the most refined mathematical artifices. This 
problem has lately been presented (it is believed) as one of 
the prize questions of the French Academy of Sciences. 
Were it however solved with all the conditions that have 
been assigned, this would not be sufficient ; since there is 
another cause of disturbance, perhaps more active than any 
yet enumerated, namely, the condensation of the vapor 
which arises from the surface of the ocean and is carried to 
different parts of the earth by the currents described. We 
owe to Mr. Espy, of this country, the principal develop- 
ment of the action of this agent in modifying and controll- 
ing atmospheric phenomena. The heated air which ascends 
at the equator is saturated with moisture, which it has ab- 
sorbed in its passage over the northern and southern oceans. 
As it ascends above the surface of the earth it meets contin- 
ually with a diminished temperature; and as the sun daily 
declines into the west, a considerable portion of it is con- 
verted into water which returns to the surface in the form 
of rain. The greatest effect of this action is immediately be- 
neath the sun ; and hence the belt of inter-tropical rains 
oscillates to the north and south with the course of the sun 
in its annual changes of declination. A portion however 



•56 WRITINGS OP JOSEPH HENRY. [185S- 

of the same vapor is probably carried by the upper current 
far beyond the tropics, and deposited in fertilizing rains even 
at the extremities of the polar circles. 

The condensation of the vapor which ascends in the equa- 
torial regions evolves an astonishing power, in the form 
of heat, accelerating the upward motion of the air, and 
modifying in a greater degree than almost any of the causes 
we have heretofore mentioned, the primary motion due 
simply to the difference of heat between the f)oles and the 
equator. To understand this, it is sufficient to refer to the 
great amount of heat contained in a given amount of steam; 
and for illustration let us suppose the following simple ex- 
periment: A quantity of water at the temperature of melting 
ice is placed in a vessel over a lamp, which is so adjusted as 
to impart one degree of heat to the water in each minute of 
time. If the process is properly conducted, the heat will con- 
tinue to increase, and, in accordar\ce with the supposition 
we have made, the water at the end of about twelve hundred 
minutes will be all converted into vapor. If the process has 
been so conducted that a degree of heat has been given to 
the liquid in each minute of tiDae, the steam will evidently 
contain about twelve hundred degrees of heat above the zero 
of Fahrenheit's scale. The greater portion of this will be. in 
what is called a "latent" state; but it will all re-appear, as 
is well known from abundant experiments, when the vapor 
is re-converted into water. From these data it is easy to 
prove mathematically that every cubic foot of water which 
falls on the surface of the earth in the form of rain leaves in 
the air whence it descended sufficient heat to produce at 
least 6,000 cubic feet of expansion of the surrounding at- 
mosphere beyond the space which the vapor itself occupied. 
The ascensional force evolved by this process must evidently 
be immense, when we consider the great amount of rain 
which falls within the tropics. A similar power is evolved 
whenever rain falls; and this principle, which has been so 
ably developed by Mr. Espy, is undoubtedly a true and suf- 
ficient cause of most of the violent and fitful agitations of 
the atmosphere which have so long puzzled the scientific 



-1859] WRITINGS OP JOSEPH HENRY. 57 

world. It however in its turn will probably require the 
consideration of modifying conditions in its applications; 
and while at present the data are known with sufficient pre- 
cision to warrant the assumption of the evolution of the im- 
mense force we have mentioned, they are not in all cases 
sufficientlj' well determined to enable us to predict, with 
numerical accuracy, the results which have been shown to 
proceed from them. The same principle of condensation of 
vapor and evolution of heat is fertile in the explanation of 
the approximate cause of rain : for example, so long as the 
wind blows over a surface of-uniform height and tempera- 
ture, there is no cause to" induce it to precipitate its vapor ; 
but if in its course it should meet a mountain, the slope of 
which it is obliged to ascend, the vapor will be condensed 
on the windward side by the cold due to the increased ver- 
tical height. The latent heat will be evolved, the circum- 
ambient air will be abnormally heated, and an upward 
motion will ensue, towards which air will flow with increas- 
ing velocity to restore the equilibrium of the ascending 
column. In this way Mr. Espy explains very satisfactorily 
the fact that the wind blows over the desert of Sahara to 
supply the diminished pressure occasioned by the rains over 
the windward side of the Himalaya mountains. The same 
principle is immediately applicable to the explanation of 
the rainless districts in South America, Mexico, and other 
portions of the earth. The air, as it ascends on the wind- 
ward side of the mountains, deposits its moisture ; and if the 
elevation is sufficiently high, it will pass over in a desiccated 
condition. 

The idea that mountains attract vapor is not founded on 
any well established principle of science. Molecular attrac- 
tion extends only to imperceptible distances, and the attrac- 
tion of gravitation is too feeble a force to produce results of 
this kind. The evaporation of water, and the transfer and 
subsequent condensation of the vapor in other parts of the 
earth, is undoubtedly the most active cause which produces 
the continual and apparently fitful changes of the weather. 

We have stated that within the torrid zone there exists a 



58 WRITINGS OP JOSEPH HENRY. [1855- 

belt of rain, produced by the partial condensation of the 
vapor which ascends with the air of this r^on ; and since 
the sun between the 21st of March and the 21st of June 
passes from the equator to 23J degrees north, and then 
makes a similar excursion as far south, the rain v belt follows 
his course, and hence all countries within the tropics must 
have a periodical rainy season. 

The air also which flows over to the north, and which, as 
we have seen, descends to the earth in the westerly belts of 
wind, carries with it a portion of vapor, and deposits it in 
the form of rain ; and hence there is a tendency to a rainy 
and dry season beyond the tropics, which oscillates north 
and south with the varying motion of the sun. This ten- 
dency to regularity of rain is in many places masked or 
neutralized by the configuration of the country. It is how- 
ever distinctly marked on the western coast of the United 
States and of Europe, as well as in various other places in 
the north temperate zone. Oregon and California have 
their rainy belt, which descends to the south in the winter, 
and again returns in the spring. In Lisbon, the number of 
rainy days in December is 15, to 2 in July ; in Palermo, 17 in 
December, to 2 J in July. In Algiers, which is also north of the 
tropic, but farther south, from the average of ten years, there 
arc 18 rainy days in January, and on the other hand, only 
a single one in July. Another fact of interest with regard 
to the extra-tropical belt of rain is that it commences sooner 
at greater elevations above the surface : for instance, at the 
peak of TenerifiFe, the rainy season commences at the top a 
fortnight earlier than at the bottom ; so that while rain is fall- 
ing in abundance on the summit, the country in the vicinity 
of the mountain, at the level of the sea, is enjoying sunshine 
and a balmy atmosphere. According to Mr. Espy's views, 
the latter results from the radiant heat given off by the con- 
densing vapor above. The sun however descending still 
farther tothesouth brings down the rain belt to the level of the 
earth in this latitude, and the rainy season then commences. 
Similar phenomena have been observed on the higher parts 
of the Coast range of mountains of California ; and indications 



18591 WRITINGS OF JOSEPH HENRY. 50 

of a like action are witnessed on the higher peaks of the 
Appalachian chain. Besides the causes of the general per- 
turbations of the atmosphere, which we have thus given in 
considerable detail, some authors have added magnetism and 
electricity, and others have indeed attributed some of the 
principal efiFects we have mentioned to these agencies ; but 
the present state of science does not warrant us in consider- 
ing these as true or suflBcient causes, except in the case of 
thunder storms, and perhaps tornadoes, in which the elec- 
tricity evolved by the action of the storm itself may modify 
some of the results. Electricity however probably plays a 
subordinate part ; since it is itself a consequence, and not a 
cause. 

Terrestrial magnetism has not been shown in any case to 
affect meteorological phenomena; it is a force which never 
produces translation, but merely direction of the needle. 
The air in its natural condition is not magnetic in the proper 
sense of the term, any more than a piece of steel wire is so 
before the power has been developed in it by a magnet. 

We are not allowed in strict scientific investigations, to 
explain a phenomenon by referring it to any agent, unless 
we show, in accordance with the laws of that agent, that it is 
capable of producing the result; and consequently magnet- 
ism is here not admissible. 

Ourrents of the Ocean. — We have seen the effect of the un- 
equal heating of different parts of the earth by the sun in 
giving rise to great gyrations of air ; and it must be evident 
that there is a tendency to produce a similar result in the 
aqueous envelope of the globe. Let us first suppose the ocean 
to cover the whole earth to a uniform depth, and to be unin- 
terrupted by continents. If the earth were at rest and the 
heat of the surface at the equator could extend down suflS- 
ciently into the depths of the water, the latter would bo 
expanded and would stand higher in the equatorial regions 
than in those of the poles; a current therefore, as in the 
case of the air, would be established toward the north and 
south, from the equator, which would be cooled in its pas- 
sage, would sink to the bottom, and return again to its 



'60 WRITINGS OF JOSEPH HENRY. [1855- 

starting point, to commence the same course anew. If we 
now suppose the earth, as in the case of the atmosphere, 
to be put in motion around its axis towards the east, the bot- 
tom currents, or those flowing towards the equator, coming 
from a part of the earth moving slower to a part going faster, 
would fall behind, and thus assume a westerly direction. 
They would therefore ascend obliquely in a westerly direc- 
tion towards the surface, flow back towards the pole, (in their 
course curving constantly towards the east,) and as they 
cooled would sink down towards the bottom, to return again 
to the equator. Different portions of the upper surface of 
the current, as in the case of air, would continue their 
northerly course obliquely, and descend at intervals, some 
reaching nearly to the poles. 

The result of the whole of this action would be a series 
of gyrations to the north and south, with the upper portion 
turned towards the west, forming a continuous circuit at the 
equator round the whole earth in a westerly direction, and 
a circuit in each temperate zone from the west. This would 
be the result, if the water could be heated to a sufficient 
depth; and accordingly it is considered by some that heat- 
ing the water is the principal cause of the currents of the 
ocean, — on which account I have so described it. Yet 
though doubtless a true — I do not consider it a sufficient — 
cause; but I would ascribe the currents of the ocean mainly 
to the action of the winds in the belts of the equator and 
in the two temperate zones. 

The constant westerly winds on either side of the equator 
would tend to produce a westerly current around the earth, 
provided no obstructions existed to its free course ; but if, 
instead of considering the earth as entirely covered with 
water, we suppose the existence of two continents, extend- 
ing from north to south, forming barriers across the current 
we have described, and establishing two separate oceans, 
similar to the Atlantic and Pacific, then the continuous cur- 
rent to the west would be deflected right and left, or north 
and south, at the western shore of each ocean, and would 
form four immense circuits, namely, two in the Atlantic, 



-1859] WRITINGS OP JOSEPH HENRY. 61 

9 

one north and the other south of the equator, and two in 
the Pacific, similar in situation and analogous in direction 
of motion. For a like reason there will be a tendency to 
produce a similar whirl in the Indian ocean, the current 
from the east being deflected down the coast of Africa, and 
returning again into itself along a southern latitude on the 
western side of Australia. Besides these great circulating 
streams, the water supplied by all the rivers emptying into 
the Arctic basin, as well as that from all the precipitation in 
this region, returns to the south, and by the motion of the 
earth must tend westwardly in a current along the eastern 
shore of each continent between it and the stream flowing 
to the north. Similar currents, but more difiuse and less in 
amount, must constantly flow from the Antarctic regions. 

We do not mean to assert that these whirls can be contin- 
uously traced on the surface of the ocean, though by attent- 
ively examining the maps their general outline may be 
marked out. We wish to convey an idea of the general tend- 
ency of the motions of the aqueous covering of the globe — 
the central thought, as it were, on which they depend. The 
regularity of their outline will be disturbed by the configu- 
ration of the deflecting coasts and the form of the bottom of 
the sea, as well as by islands, irregular winds, difference of 
temperature, and above all, by the annual motion of the 
sun as it changes its declination. The effect of these cur- 
rents in modifying the climate of different parts of the world 
has long been recognized, though the detail of the mode in 
which this is produced has not until recently been pointed 
out. The Gulf Stream of the North Atlantic carries the 
warm water of the equator beyond Iceland and the northern 
extremity of Europe, and it may even be traced to the 
shores of Nova Zembla. Without its influence the climate 
of Norway, Great Britain, and the western coast of Europe 
would be as cold as that of the corresponding parallels of 
latitude on the North American continent. In like manner, 
the great circuit of the waters of the Pacific conveys the 
warmth of the equator along the eastern coast of Asia to 
Kamtchatka, and gradually cooling in its course, descends 



62 WRITINGS OP JOSEPH HENRY. [1855- 

aloiig the northwest, ooast of tlie North American continent, 
to receive a new accession of heat and be again conveyed to 
the north. Tlie total result of this circulation together with 
those of lesser influence in the northern hemisphere, is 
shown in the annexed polar projection, in which the series of 
irregular linos, marked 50°, 32°, 16°, and 0°, indicate the 
mean annual temperature of the points through which they 
pass, and are called the yearly isothermal lines, or lines of 
equal licat. 




The darker line, marked 32°, indicates the boundary of 
the region within which the avernge temperature is below 
the freezing point. It will bo seen at a glance that, instead 
of being circular in its outline, it has the form of an irreg- 
ular elongated ellipse, the greater diameter of which is across 
the pole, from tlie southern extremity of Hudson's Bay to 



-1859] WRITINGS OF JOSEPH HENRY. 63 

the south of Lake Baikal, in Siberia. It extends some de- 
grees lower to the south in Asia than in America. The 
shorter diameter of the ellipse is at right angles to the longer, 
and passes from near Behring's Straits, through the pole, to 
the open ocean west of Norway. Its longer diameter is 
nearly twice that of its shorter, and is in the direction of the 
greatest amount of land in the polar regions. This form of 
the curve and the peculiarities of the other curves are due 
principally to the currents of the Atlantic and Pacific oceans 
transporting the water from the equatoi: to the north, and 
carrying with it the higher temperature. An elliptical 
dotted line will be perceived in the polar regions, the centre 
of which does not coincide with the geometrical axis of the 
earth, but is nearer the continent of North America than 
that of Asia, thus indicating that the coldest point on the 
earth's surface is a number of degrees south of the pole. It 
is true, this region has never been visited by man ; yet know- 
ing the law of the diminution of heat, and the form of the 
other lines, the smaller one can be drawn with considerable 
accuracy. It may be interesting to remark in this place 
that the mean temperature of the coldest part of the north- 
ern hemisphere has almost exactly the temperature of the 
zero of Fahrenheit's scale; a somewhat curious although en- 
tirely accidental co-incidence. 

We have thus far almost exclusively confined our remarks 
to the general principles of science on which the phenomena 
of meteorology depend; we shall now give special attention 
to the application of these principles to the peculiarities of 
the climate of the continent of North America, and more par- 
ticularly to that part of it which includes the territory of the 
United States. For this purpose it will be necessary to give 
a brief sketch of the topography and surface of the country. 

Physical Geography of the Uait'ed States. — The climate of a 
district is materially affected by the position and physical 
geography of the country to which it belongs. Indeed, 
when the latitude, longitude, and height of a place above the 
sea, are given, and its position relative to mountain ranges 
and the ocean is known, an approximate estimate may bo 



64 WHITINGS OF JOSEPH HENRY. [18S5- 

formed as to its climate. The North American conthient 
extends across nearly the whole breadth of the nominal tem- 
perate zone, and has an average width of more than fifty de- 
grees of longitude. The general direction of the eastern 
coast of the United States lies in a great circle passing 
through Great Britian. Hence, a ship, while sailing along 
this coast, is on its direct route to the British Isles. This 
fact — which is not clearly exhibited on the flat surface of 
a map, but is shown on the convex surface of a globe — has 
a bearing, not only on commerce, but also on the direction 
of the Gulf Stream, which conforms to the general direction 
and sinuosities of the coast. It will be seen by the map,* 
(to which frequent reference is here made), that the eastern 
coast of the United States exhibits three great concave curv- 
atures; the first commencing at the extremity of Florida, 
and extending to Cape Hatteras; the second, from Cape 
Hatteras to Cape Cod ; and the third, from Cape Cod to Cape 
Sable. These broad ocean bulgings, or bays, have a marked 
influence on the cold polar current which descends along 
the coast, and also, as has been shown by Professor Bache, on 
the great tide-wave of the Atlantic ocean, as it approaches 
our shore. At the southern extremity of the United States 
is the great elliptical biisin containing the perpetually 
heated waters of the Gulf of Mexico, an enormous steximing 
cauldron continually giving off an immense amount of va- 
por which, borne northward by the wind of the southwest, 
gives geniality of climate and abundant fertility to tlie east- 
ern portion of our domain. On the western side of the con- 
tinent the coast presents, as a whole, an outline of double 
curvature, principally convex to the west in that part which 
is occupied by the United States, and concave further north. 
These bends of the coast-line and of the adjacent parallel 
mountain ridges affect the direction of the winds in this quar- 
ter and consequently of the ocean currents. The Gulf of 
California at the south, between the high mountains of the 
1 eninsula of that name and those of the main land, must also 
materially modify the direction of the wind in that region. 

*[See Map, nt page 72.] 



-1859] WRITINGS OF JOSEPH HENRY. 65 

The continent of North America is traversed in i\ north- 
erly and southerly direction by two extensive ranges of moun- 
tains — the Alleghany system on the cast and the Rocky 
Mountain system on the west. We give the latter name to 
the whole upheaved plateau and all the ridges which are 
based upon it. These two systems separate from each other 
more widely as we pass northward, and between them is the 
broad interval which, within the territory of the United 
States, is denominated the -valley of the Mis3issippi; but in 
reality the depression continues northward to Hudson's Bay, 
and even to the Arctic ocean, giving free scope to the winds 
which may descend from that inhospitable region. It how- 
ever may be divided into two great basins, one sloping 
towards the south, comprising the basin of the Mississippi, 
and the other sloping to the north, including the basins of 
Mackenzie's river and of Hudson's Bay, the dividing swell 
which may be traced along the heads of the streams having 
an elevation of about 1,200 feet. Our remarks must be prin- 
cipally confined to the portion of the continent south of the 
49th degree of latitude. 

The swell of land or watershed, on which the Alleghanies 
are situated, has an average elevation of at least 3,000 feet, 
although the ridges and mountains based upon it rise to a 
much higher elevation. The loftiest point is Clingman's 
Peak, of the Black Mountains in North Carolina. It. has 
lately been measured by Prof.Guyot, and is found to have 
a height of 0,702 feet. The next greatest elevation is Mount 
Washington, the highest peak of the White Mountains, in 
New Hampshire, which, according to the same authority, 
has an elevation of G,285 feet. The lowest depression in this 
watershed, with the exceptions to be next mentioned, is in 
Pennsylvania, and has an elevation of a little less than 
2,000 feet. Further north the whole system is cut through 
by the valley of the Hudson nearly to its base, and also by 
the valley of the St. Lawrence. The latter, together with 
the basins of Lakes Ontario and Erie, forms a narrow trough 
between the Atlantic and the Mississippi valley, along which 
the flow of air may locally affect the climate. The position 

6-2 



66 WRITINGS OF JOSEPH HENRY. [1855- 

of the Alleghany Mountains however does not so much 
aflTect the meteorology of the country as from the magni- 
tude of the system we might at first suppose; and this re- 
sults from the fact that their direction is from the southwest 
towards the northeast, which as we shall see hereafter, is the 
prevailing direction of the fertilizing wind of the United 
States. They do not therefore obstruct its course; it flows 
on either side of them and along the valleys between them. 
They do however in a considerable degree, modify the 
character of the westerly winds as felt upon the coast, de- 
priving them of their moisture. 

A reference to the map will show that the Rocky Moun- 
tain system occupies one-third of the entire breadth of the 
United States, and that the remaining two-thirds are divided 
into two nearly equal portions by the Mississippi river, be- 
ginning at its source. This great western mountain system 
of the North American continent, which produces the most 
important modifying influence on the climate of the United 
States, may be described as a broad, elevated swell or plateau 
of land, (the prolongation of the system of South Amer- 
ica, to which the Andes belong,) extending northward 
in the general direction of the Pacific coast, with varying 
elevation and width to the Arctic circle. It occupies nearly 
the whole breadth of Mexico, from the Rio del Norte to the 
Pacific, and becomes still broader as it extends northward, 
occupying at the latitude of 40°, (as has just been said,) one- 
third of the breadth of the whole continent. Resting upon 
this great swell of land is a series of approximately parallel 
ridges, the principal of which are the Rocky Mountain 
ranges on the east and the Coast ranges on the west, with 
ridges of less magnitude between, the general direction of 
which is north, inclining towards the west. Between these 
ranges is a series of extensive elevated valleys of extreme 
dryness, and, in the summer, of intense heat. 

As we proceed north from the high plains of Mexico, the 
base of the system declines to about the 32d parallel of north 
latitude, where its transverse vertical section presents the 
least amount of land above the general level. It has how- 



-1859] WRITINGS OF JOSEPH HENRY. 67 

ever an average elevation in the principal part of about 
4,000 feet, and the lowest notch or pass in the ridge on the 
eastern side is 5,717 feet above the ocean. Along the 35th 
parallel the vertical section across the mountain system is 
considerably greater in width and elevation. The general 
height above the ocean is at least 5,500 feet, and the lowest 
pass of the principal ridge is here 7,750 feet. The section 
of the system between the parallels of 38° and 40° has an 
elevation of 7,500 feet, and the lowest notch in the principal 
ridge is 10,032 feet above the level of the sea. From this 
section, as we pass to the north, the altitude and width 
decline; and along the parallel of about 47° the mountain 
base is much contracted in breadth, and has a general alti- 
tude of 2,500 feet. The lowest pass however of the most 
elevated ridge of this section is 6,044 feet We have no 
definite information as to the mountain base north of this 
line. It appears however to continue at a lower elevation, and 
consequently to produce less influence upon the climate of 
the country to the east of it than the portion within the 
boundary of the United States. 

From the eastern edge of what we have called the moun- 
\mn system — that is from the foot of the Rocky Mountain 
chain to the Mississippi river — a space comprising, as was 
said before, about one-third of the whole breadth of the 
United States, the surface consists of an extended inclined 
plain, which slopes eastward to the Mississippi and south- 
ward to the Gulf of Mexico, having at the greatest elevation, 
near the intersection of the parallel of 40° and longitude 105°, 
a height of upwards of 5,000 feet, whence it gradually de- 
clines to the Mississippi river to about 1,000 feet. At the par- 
allel of 35° it has very nearly the same elevation; and thence 
it slopes to the bed of the Mississippi to about 450 feet, and 
south to the level of the sea at the Gulf of Mexico. This 
extended plain is traversed by a number of approximately 
parallel rivers flowing eastward and southward to the Missis- 
sippi river and the Gulf of Mexico, which have their rise 
principally in the mountain system, and are chiefly supplied 
by the melting of the snow and the precii)itation of vapor 



68 WRITINGS OF JOSEPH HENRY. [1855- 

which takes place at the summit of the ridges. The rivers 
are sunk deeply below the general surface of tlie plain, and 
give no indication of their existence from a distance, except 
the appearance of the tops of the cotton-wood trees which 
skirt their borders. The surface towards the southeast is 
slightly diversified by a low range of mountains, denomi- 
nated the Ozark, which probably have some slight influence 
on the local climate of Kansas. 

General Clw/rader 0/ the Surface, — The general ch^acter 
of the soil between the Mississippi river and the Atlantic 
is that of great fertility, and as a whole, in its natural con- 
dition, with some exceptions at the west, is well supplied 
with timber. The portion also on the western side of the 
Mississippi as far as the 98th meridian, (including the States 
of Texas, Louisiana, Arkansas, Missouri, Iowa, and Minne- 
sota, and portions of the Territories of Kansas and Nebraska,) 
is fertile, though abounding in prairies and subject occa- 
sionally to droughts. But the whole space to the west, 
between the 98th meridian and the Rocky Mountains, denom- 
inated the Great American Plains, is a barren waste, over 
which the eye may roam to the extent of the visible horizon 
with scarcely an object to break the monotony. From the 
Rocky Mountains to the Pacific, with the exception of the 
rich but narrow belt along the ocean, the country may also be 
considered, in comparison with other portions of the United 
States, a wilderness unfitted for the uses of the husbandman; 
although in some of the mountain valleys, as at Salt Lake, 
by means of irrigation a precarious supply of food may be 
obtained sufiicient to sustain a considerable population, pro- 
vided they can be induced to submit to privatione from 
which American citizens generally would shrink. The por- 
tions of the mountain system further south are equally in- 
hospitable, though they have been represented to be of a 
different character. In traversing this region whole days 
are frequently passed without meeting a rivulet or spring 
of water to slake the thirst of the weary traveller. Dr. 
Lethcrman, surgeon of the United States army, at Fort De- 
fiance, describes the entire country along the parallel of 35° 



-1859] WRITINGS OF JOSEPH HENRY. 69 

as consisting of a series of mountain ridges, with a general 
direction north and south inclining to the west, and broken 
in many places by deep cracks, as it were, across the ridge, 
denominated canons, which afford in some cases the only 
means of traversing the country, except with great labor 
and difficulty. The district inhabited by the Navajo Indians 
has had the reputation of being a good grazing country, 
and its fame has reached the eastern portions of the United 
States; but taking the region at large, it will be found that 
with regard to abundance of natural pasturage, it has been 
vastly over-rated, '* and we have no hesitation in stating," says 
the same authority, " that were the flocks and herds now be- 
longing to the Indians doubled, they could not be sustained. 
There is required for grazing and procuring hay for the con- 
scimption of animals at Fort Defiance, (garrisoned by two 
companies, one of which is partly mounted,) fifty square 
miles; and this is barely sufficient for the purpose." The 
barrenness and desolation so inseparably connected with 
immense masses of. rocks and hills scantily supplied with 
water are here seen and felt in their fullest extent. Dr. 
Antisell, geologist to one of the exploring expeditions, de- 
scribes the country along the parallels of 32° and 33° as 
equally deficient in the essentials of support for an ordinary 
civilized community. On the west, within these parallels, 
occurs the Great Colorado desert, extending to the river of 
the same name, which empties into the Gulf of Califor- 
nia. From the southern portion of the Colorado river, which 
is generally regarded as the eastern edge of the Colorado 
basin, the land rises eastward by a series of easy grades 
until the summit of the main ridge of the mountain system 
is gained, at a point about 500 miles east of that river. For 
the first 250 miles the ascent is across a series of erupted 
hills of comparatively recent date, and similar in constitu- 
tion to the line hills and ridges which are dotted over the 
various levels of the basin country. The entire district is 
bare of soil and vegetation, except a few^ varieties of cactus. 
Over the greater portion of the northern part of Sonoraand 
the southern part of New Mexico sterility reigns supreme. 



70 WRITINGS OF JOSEPH HENRY. [1855- 

At the mountain bases may exist a few springs and wells, 
and in a few depressions of the general level of the surface 
sloping to the Pacific may be grassy spots; but such are the 
exceptions. A dry, parched, disintegrated sand and gravel 
is the usual soil, completely destitute of vegetable matter 
and not capable of retaining moisture. The winter rains 
which fall on the Pacific coast, west of the CJoast range of 
mountains, do not reach to the region eastward. This is 
partly supplied with its moisture from the Gulf of California, 
but chiefly by the southeast wind from the Gulf of Mexico, 
flowing up between the ridges of mountains. We hazard 
nothing in saying that the mountains, as a whole, can be of 
little value as the theatre of civilized life in the present 
state of general science and practical agriculture. It is true 
.that a considerable portion of the interior is comparatively 
little known from actual exploration; but its general char- 
acter can be inferred from that which has been explored. 
As has been said before, it consists of an elevated swell of 
land covered with ridges running in a northerly direction 
inclining to the west. The western slopes, or those which 
face the ocean, are better supplied with moisture and con- 
tain more vegetation than the eastern slopes; and this in- 
creases as we approach the Pacific, along the coast of which, 
throughout the whole boundary of the United States to the 
Gulf of California, exists a border of land of delightful cli- 
mate and of fertile soil varying from 50 to 200 miles in 
width. The transition however from this border to a parallel 
district in the interior ig of the most marked and astonish- 
ing character. Starting from the sea-coast and leaving a 
temperature of 65°, we may, in the coui-se of a single day's 
journey in some cases, reach an arid valley in which the 
thermometer in the shade marks a temperature of 110°. 
We have stated that the entire region west of the 98th degree 
of west longitude, with the exception of a small portion of 
western Texas and the narrow border along the Pacific, is a 
country of comparatively little value to the agriculturist; 
and perhaps it will astonish the reader if we direct his at- 
tention to the fact that this line, which passes southward 



-1859] WRITINGS OF JOSEPH HENRY. 71 

from Lake Winnipeg to the Gulf of Mexico, will divide the 
whole surface of the United States into two nearly equal 
parts. This statement, when fully appreciated, will serve to 
dissipate some of the dreams which have been considered as 
realities as to the destiny of the western part of the North 
American continent. Truth however transcends even the 
laudable feelings of pride of country; and in order properly 
to direct the policy of this great confederacy, it is necessary 
to be well acquainted with the theatre on which its future 
history is to be enacted and by whose character it will mainly 
be shaped. 

Temperature. — Let us now consider the distribution of tem- 
perature of the wide belt across the continent of North 
America which forms the territorv of the United States. 
To illustrate this, attention is requested to the lines drawn 
from east to west across the small map so frequently refer- 
red to. These it will be seen, are of three kinds: first, 
the full line, indicating the mean or average temperature 
of the year; second, the broken line, denoting the mean 
temperature of summer; and third, the dotted line, that of 
winter. These lines are drawn through portions of the 
earth's surface having equal temperatures for the periods 
mentioned, and are plotted from the result of numerous 
observations. They do not however in all cases exhibit the 
actual temperature of the surface ; for in order to show their 
relations and render them comparable with each other and 
with similar lines in other parts of the world, it is necessary 
that the observed temperatures in elevated positions should 
be reduced to that of the level of the sea; [ind in the con- 
structibn of this map allowance has consequently been made 
for decreasing temperature of one degree for every 333 feet of 
altitude. Th6 map therefore will present to the eye the lines 
along which the temperature of the air would be equal for 
the periods mentioned, were we to suppose the mountain 
ranges entirely removed and the air brought down to the 
level of the ocean. 

These lines, at a glance, exhibit remarkable curvatures, 
particularly in the western portion of the United States, indi- 



WRITINGS OP JOSEPH HENRY. [1859- 



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74: WRITINGS OF JOSEPH HENRY. [1855- 

temperature of a place is nearly equal to 70° instead of 60°, 
since the curve of 70° reaches almost as far north. The 
curve of the mean temperature of 60°, as has been stated, 
terminates on the shores of the Pacific, at about latitude 34° ; 
whereas, on the Atlantic, it commences at about 37°, indi- 
cating a lower temperature along the 35th parallel of lati- 
tude on the Pacific than on the Atlantic shore. The next is 
the curve of 70°. This commences in about latitude 28° on 
the coast of Florida, passes through New Orleans, and thence 
to a point on the Pacific in the latitude of 30°. It presents 
an upward curvature in that portion which passes through 
the Gulf, indicating that New Orleans is warmer than a cor- 
responding place on the Atlantic, or on the shores of Texas. 
It thence curves rapidly to the north, though indicating the 
greatest temperature near the eastern edge of the mountain 
system. It terminates on the Pacific at a point at least two 
degrees higher than its point of commencement on the At- 
lantic, thereby indicating that along the 30th parallel the 
mean temperature is a little greater on the east than on the 
west side of the continent. It should be constantly borne in 
mind, that the temperatures in these descriptions are those 
which would be exhibited were the mountain system of the 
country removed and the whole reduced to the level of the 
ocean. This system of lines therefore exhibits the extraor- 
dinary fact that eliminating the effect due to elevation, there 
remains a cause of a remarkable degree of abnormal heating 
beyond that due merely to the latitude of the place. In 
other words, that at every point within the mountain system, 
whatever may be its elevation, the temperature is far above 
that of the same elevation of a point in free space having the 
same latitude, when compared with the eastern and western 
coast. 

The broken lines indicate the temperatures of summer. 
The first of these given on the map is that of 70° and com- 
mences near Long Island, ascends rapidly towards the north, 
and then descends towards the large lakes, passing through 
Lake Erie; it reaches its greatest northern declination at 
about the 110th meridian, and thence turning nearly paral- 



•1859] WRITINGS OF JOSEPH HENRY. 75 

lei to the coast, meets the Pacific in the latitude of about 34°. 
The portion of this curve along the coast of the Pacific shows 
the remarkable fact that the summer temperature is nearly 
the same from latitude 32° to 45°, or through a distance of 
13 degrees, the whole having the same temperature as that 
of 41° on the Atlantic coast. This curve also clearly ex- 
hibits the great effect which the vicinity of the lakes has on 
the temperature of summer. While the dark lines indicat- 
ing the mean temperatures of 40° and 50° are not at all 
affected by their proximity to these large bodies of water, tlie 
mean temperature of the summer is materially reduced. We 
may here call attention to the fact that the dotted line, de- 
noting the winter, suddenly bends up at the same place, in- 
dicating an increase of temperature due to the vicinity of the 
same reservoirs of water. The line of 80° commences near 
Charleston, South Carolina, and extends rapidly upward 
through the valley of the Mississippi, thereby indicating that 
the temperature of summer in the interior, along this paral- 
lel, is much higher than on the seaboard. The western por- 
tion of this curve also exhibits great intensity of summer 
heat in the mountain system, and a remarkable degree of 
uniformity along the coast range of mountains parallel to the 
Pacific. The short lines of 82°'5 and 85° denote a high tem- 
perature of uniform intensity, extending to the north, and 
indicate the great summer heat of the western plain. 

It will be seen, by examining the dotted lines, that the 
temperature of winter in the middle of the Mississippi valley, 
about the 95th meridian, is lower than on either the eastern 
or western coast ; also, that the line of 30°, which is only two 
degrees below freezing, starts at the east end of Long Island, 
passes through Lake Erie, thence down to the 40th parallel, 
in longitude about 91°, and thence rapidly rises to the north, 
and leaves the United States at the 118th meridian. The 
line of 40° of winter temperature commences at the mouth 
of the Chesapeake, follows nearly the same general direction, 
and meets the Pacific Ocean near Puget's Sound, indicating 
the remarkable fact that this place and Norfolk, on the 
Atlantic, have about the same winter temperature. The line 



76 WRITINGS OP JOSEPH HENRY. [2B55- 

of 50^ is also similar to that of the last; also the line of 
60°, which indicates in the Gulf of Mexico a lower degree 
of temperature in winter than exists on the Atlantic or 
Pacific coasts. In examining these winter lines attentively, 
it will be seen that the rise is not uniform from the 95th to 
the 105th degree, but the bend is most sudden about the 
103d; which is probably caused by the occasional descent 
along this region of the polar winds to the Gulf of Mexico. 

It has been stated that in reducing the lines to the level 
of the sea, 333 feet of elevation have been taken for each 
degree of Fahrenheit's scale. Therefore the actual tempera- 
ture of any part of the United States may be readily deter- 
mined, provided its elevation above the sea is'known, by 
subtracting from tlie temperature given on the chart as many 
degrees as there are spaces of 333 feet in the elevation. Let 
us take, for example, the junction of the Kansas with the 
Missouri river, on the 95th meridian. This point, it will 
be seen by inspecting the map, is midway between t^e mean 
isothermal lines of 50° and 60°, and its temperature will 
therefore be approximately 55°. It has an elevation of 
about a thousand feet, which will give three degrees for the 
reduction ; and hence its temperature will be about 52°. 

On a little reflection it will be clear that it would have 
been impossible to draw these lines on the uneven surface 
of the earth. The variation of temperature due to height 
would mask that due to latitude and other climatplogical 
causes. For example, a greater elevation of mountain peaks 
at the south would represent a colder local temperature than 
regions further north, would entirely hide from view the re- 
sults which are due exclusively to the peculiarities of con- 
formation of the country, and would give no means of com- 
parison. 

Winds of North America. — We have said that the whole 
mountain system of the western portion of the United States 
presents a remarkable abnormal elevation of temperature 
above the eastern and middle portions of the continent, and 
the question naturally presses itself upon us as to the cause 
of this surprising difference. The simple statemant that the 



-1859] 



WBITINOS OF JOSEPH HENKV. 



77 



western side of Europe is also warmer tlmn the eastern side 
of Asia does not explain the phenomenon ; it merely points 
out an analogy, bul not a cause. It is evident that the posi- 
tion of the mountain system, and the direction of the ridges 
with reference to the prevailing winds, must have some con- 
nection with this phenomenon. In addition to this, the 
westerly aerial current, as it is principally derived from the 
equatorial regions, must in itself be warmer than the tem- 
perature due to the latitude of the belt in which it is mov- 
ing. It will he well, therefore, before proceeding to this 
branch of the subject, to give a brief statement of some of 
the results which have been reached by deductions from 
■ actual observations in regard to this powerful agent in mod- 
ifying climate. For the materials used for this purpose we 
are indebted to the valuable labors of Prof. James H. Cofhu, 
of Lafayette Coltege, the results of which have'been pub- 
lished by the Smithsonian Institution.* 

In order that the facts may be the more readily compre- 
hended, and produce a more indelible impression upon the 
mind, since ideas received through the eye are the most defi- 
nite and lasting, we shall represent the direction and amount 
of the wind by means of diagrams such as are exhibited in 
the accompanying figures. The lines indicated by tlie letters 
JV. E.- S. W. represent the cardinal points of the compass, 
and the breadth of shading along any of these lines the rel- 
ative amount of wind in the coarse of a given period ob- 
served at a particular place. 

Thus for example in No. 1, in the circle on the right hand 
No. 1. 




•["The Windaof the Northern Hemiflphere," 4to. 198 pp. 13 maps 
tud phitei. Smithwniui CoAtribuUons to Knowledge; vol. ti.] 



78 



WRITINGS OF JOSIi:PH HUNRY. 



[1855- 



sidc, tho shading represents tlio amount of wind from the 
different points of the liorizon during the winter mouths 
in New England, from the average of a large number of ob- 
servations at different places. Hence it will be seen that the 
predominant wind during tho winter, in this part of the 
United States, is from the northwest; the next in amount is 
from the northeast and southwest, the eastern and south- 
eastern portion of the horizon during the winter exhibiting 
but little wind. The next eircle to the left shows the great 
preponderance of wind in New England from the south- 
west during the summer. Tho winds exhibited in the two 
circles combined will produce a general resultant from the 
west. The next circles to the left exhibit the amount of wind 
in summer and winter in tlie State of New York. In winter 
the greatest amount is from the northwest, and in summer 
from the southwest. 

No, 2 presents the winds in Penusylvania, and in Illinois, 
Wisconsin, and Iowa. 

No. 2. 

lUinoia, Wiacoiuin, louxr, PeHnaylvania. 

Summer. Winter. Summor. Winter. 




From these it will be seen that in Pennsylvania the wind 
is more westerly in winter than in New England, but still 
tlic greatest amount is from a point north of west. In sum- 
mer tlie greatest amount is found a little soutli of west. 
During winter in the States of Illinois, Wisconsin, and Iowa, 
generally, the greatest prevalence is from the nortliwest, and 
in summer from the west and south. The maximum is a 
little east of south; the southwestern half liowever of the 
horizon in both seasons lists the greatest amount. 

The circles in No. 3 indicate that in Nebraska and Kan- 
sas tho greatest amount of wind in the winter is from the 



-lass] 



WRITINGS OF JOSEPH HENRY. 



70 



northwest, and in the summer from the southwest. In 
Or^on and Washington Territories the greatest amount of 

No. 3. 




wind in the winter is from the southeast, and the next 
greatest from the northwest, these two principally dividing 
the season between them. In summer a very large propor- 
tion is from the northwest, which is a remarkable inversion 
of the winds as observed in other parts of the United States. 
The principal current in winter being in the direction of 
the coast, from the southeast, consequently tends to mitigate 
the cold; while in summer it is in the opposite direction, 
and therefore tends to produce a similar effect in diminish- 
ing the intensity of the heat. 

No. 4. 

Ttxiu and Ntw Mtxieo. S. C, Oa., Ala., Miaa. 

Smnmer. Winter. Summer. Winter- 




In No. 4 the two circles to the right exhibit the general dir- 
ection of the wind in South Carolina, Georgia, Alabama, and 
Mississippi; and those on the left, in Texas and New Mexico. 
In the former the winds in winter nearly equally divide the 
whole circumference of the horizon; in summer the south 
and southeast winds prevail. In Texas and New Mexico 
the wind in the winter ia largely from the north, and often 



f^O WBITINQS OF JOSEPH HENBY. [1859- 

from the south ; in summer its prcpoDdertuice is greatly in 
favor of the south. 

No. 5. 
Linaer CtUifon 
Sumnier. 




No. 5 exhibits the winds of Lower California, which in 
winter are from all parts of the horizon ; those from the 
north and west however preponderating. In summer it is 
almost entirely from the southwest 

The winds thus represented are surface currents, and are 
consequently much influenced by the position of mountain 
ranges. Tliis is strikingly shown in No 6, which represents 
the mean annual wind at Hudson, Albany, and Utica, in 
the State of New York. 




Hudson is in the valley of tht^Hudson river, a Igng, nar- 
row glen extending in a north ami soutli direction ; and as 
the figure indicates, the winds are principally conSued to 
the same course, blowing down the glen to the south in 
winter, and in the opposite direction in the summer. Albany 
is situated at the junction of the wide Mohawk valley with 
that of the Hudson, and the wind accordingly is from the 
northwest nnd from tlie south. Utica is in the valley of the 
Mohawk, which has a general cast and west direction, the 



-i859] WRITINGS OF JOSEPH HENRY. 81 

influence of which is 'strongly marked by the prevailing 
winds. In a like manner the direction of the wind on the 
coast of the Pacific is modified by the trend of the coast and 
the parallel mountain chains. Almost every position at 
which meteorological observations are made is liable thus 
to be affected by the local topography; but the result of this 
is eliminated in a great measure by computing the average 
direction from a number of stations within a limited dis- 
tance of each other. Yet, though in this way the opposite 
local influences in particular districts may be made to bal- 
ance each other, those of great mountain systems still remain. 
These in turn however may be merged in a series of obser- 
vations extending across continents, or entirely around the 
world. In this way, by collecting all the reliable observa- 
tions which have been made on the winds in the northern 
hemisphere, so far as they were accessible to the Smithsonian 
Institution, Prof. CoflSn has established the fact, before men- 
tioned, that the resultant motion of the surface atmosphere 
between latitude 32® and 58° in North America is from the 
west, the belt being twenty degrees wide, and the line of its 
greatest intensity in the latitude of about 45°. This how- 
ever must oscillate north and south at different seasons of 
the year with the varying declination of the sun. South of 
this belt, in Georgia, Louisiana, &c., the country is in- 
fluenced at certain periods of the year by the northeast trade 
winds, and north of the same belt by the polar winds, which 
on account of the rotation of the earth, tend to take a direc- 
tion toward the west. It must be recollected that the westerly 
direction of this belt here spoken of is principally the result- 
ant of. south westerly and northwesterly winds alternately pre- 
dominating during the year. 

From what has been stated in regard to the general circu- 
lation of the atmosphere it would appear that these winds 
are due to the returning upper currents which flow over from 
the heated region of the equator, producing a southwest, a 
west, or a northwest wind, according to the distance to which 
they extend northward before they commence to descend to 
the earth. If the sun continued on the equator during the 

G-2 



82 WRITINGS OF JOSEPH HENRY. [1855- 

year, and there were no obstacles to the free motion of these 
currents, thev would be constant in intensity and direction 
around the whole earth ; but the change in declination of 
the sun, and the obstacles opposed by continents and moun- 
tain chains, modify in an important degree the simplicity 
of this motion. When the sun ascends to the north, it 
carries with it the whole circulating system of the atmos- 
phere, causes the northeast trade winds to invade the south- 
ern part of the United States, and the inferior currents, which 
give rise to the southwest wind, to flow in summer over a 
large portion of our territory. The latter, charged with 
the vapor from the Atlantic and the Gulf of Mexico, impart 
warmtli and fertility to all parts of the surface on which 
they descend. The higher currents, which produce the west 
and northwest winds, flow in summer above us, to descend 
further to the north. Their course however is marked by the 
almost invariable direction of the upper clouds and of the 
summer thunder storms, which, in the greater part of the 
United States, pass from the west to the east. The curving 
course of the returned currents, when the sun is south of the 
equator, is perliaps best marked by the direction of the hur- 
ricanes, which exactly follow the path we have described as 
that of the particles of air in the general circulation so often 
referred to. This will be seen by examining the storm tracks 
on one of the maps of the lamented Redfield. 

It is evident, from theory as well as from every day obser- 
vation, that the currents of the belt of the northern hemi- 
sphere, in which the United States is situated, must be subject 
to many perturbing influences, and that this region is well 
entitled to the denomination of the zone of variable winds. 
While the great circulation which we have described is 
going on, particularly above us, every rain that occurs and 
every variation of temperature tends to disturb its regularity 
at the surface of the earth. According to the views here 
presented the following winds of the United States belong to 
tlie general circulation, namely, the so^ithwest, west, north- 
west, north, and northeast; while those from the opposite 
quarters of the horizon are principally due to abnormal 



-1859] WRITINGS OF JOSEPH HENRY. 83' 

atmospheric disturbances. We say principally, because a 
portion of the surface northeast trade wind in summer prob- 
ably blows over Florida and the lower part of Louisiana. 
These views have been strengthened by a series of observa- 
tions collected by M. De Done, from which it is shown that 
the winds from the western half of the horizon, as indicated 
by the clouds, preponderate over those from the east, as 
indicated by the wind vane at the surface; or in other 
words, that there is a greater tendency to a movement, even 
in our latitude, in the upper strata of air from the western 
half of the horizon, and in the lower from the eastern — a 
result in conformity with the general principles we have 
endeavored to explain. The circulation in the region of 
variable winds may often be inverted, and the compensation 
take place by means of winds in different parts of the hemi- 
sphere. It must be evident from meclianical principles that 
to balance every current of wind which flows to the north 
over any parallel of latitude along any meridian an equal 
amount must flow back to the south either along that 
meridian or some other. If the compensation takes place at 
the same meridian, one current must flow above and the 
other below. If at different meridians, the compensating 
currents may both be at the surface or both above. The 
fact that very different temperatures prevail at different parts 
of the world at the same time under the same latitude favors 
the idea of Prof. Dove that the compensation does in many 
cases take place in the latter way. Mr. Espy supposes that 
our southwest wind is produced mainly by the descent of 
the return trade winds at about the 30th parallel, and by 
rains accompanied with an elevation of temperature, and 
consequently an ascent of air at the parallel of 58® or 60°, 
and that it returns again in an upper current over the belt 
we have described towards the south. That whatever air 
reaches the polar regions should descend there and flow 
southward, and then rapidly decline to the west, appears to 
be an evident consequence of well established laws. The 
rapid inclination of the air on account of the great increase 
of rotation in the surface of the earth in this latitude would 



84 WRITINGS OF JOSEPH HENRY. [1855- 

tond to produce a wind in a westerly direction along the 
parallel of 60°, which would conflict with the currents from 
the south, and thus produce a low barometer — a tendency 
to rain — and form a natural boundary between what may 
be denominated the polar winds and the belt of westerly 
winds, due, as we have supposed, to the returning trades. 
The region of the middle belt must be one of great irregu- 
larity, occasionally encroached upon by the polar winds of 
the north on one side and the inter-tropical winds of the 
south on the other, tending to restore the equilibrium in 
some cases in the mode suggested by Prof. Dove, and again 
in that proposed by Mr. Espy. We are however inclined to 
believe that all these are perturbations in the general circu- 
lation. 

That the great western mountain system of North and 
Central America produces an important effect on these cur- 
rents cannot be doubted, when it is recollected that one-third 
of the whole atmosphere is below its higher portions. It 
prevents the northeast trade wind from passing to the coast 
of the Pacific in about the latitude of 30°, and probably de- 
flects northeastward a part of the lower portion of the upper 
return wind, giving more force and quantity to the southwest 
summer currents than they would otherwise have. This is 
the view adopted by Mr. Robert Russell, of Scotland, one of 
the most industrious and promising of the younger meteott)l- 
ogists of Europe, who visited this country about three years 
ago for investigating its climate and agriculture. It would 
appear from what has been stated before, that h northwest 
current most generally prevails in the higher regions, and 
that the southwest current is a more superficial one. Accord- 
ing to Mr. Russell, all the disturbances of the atmosphere in 
this country are produced by the unstable equilibrium oc- 
casioned by the superposition of the northwest wind on that 
of the southwest; and this, we think, in connection with the 
evolution of heat, according to the principles of Mr. Espy, 
will account for all the violent commotions of our atmos- 
phere, whether they appear in the form of winter storms, 
thunder gusts, or tornadoes. 



-1859] WRITINGS OF JOSEPH HENRY. 85 

METEOROLOGY IN ITS CONNECTION WITH AGRICULTURE. 

PART ni. — TERRESTRIAL PHYSICS AND TEMPERATURE. 

(Agricultural Report of Commissioner of Patents, for 1857, pp. 419-506.) 

We intend in this number of our contributions to Meteor- 
ology as applied to Agriculture, to give a more definite expo- 
sition of some of the general principles of science especially 
applicable to this subject than is usually met with in ele- 
mentary works. And we are lead to this by numerous in- 
quiries from correspondents in various parts of our country, 
whose interest in the study of meteorology has been awakened 
during the last few years. We trust that our essay will be 
acceptable.to the agriculturist, since however remote from his 
pursuits the theoretical partof the communication may at first 
sight appear, a proper view of the relation of science and art 
will enable him to see that the one is dependent on the 
other, and that each branch of the study of nature is inti- 
mately connected with every other. 

We take it for granted that the American farmer is cap- 
able of logical reflection ; that he is not content with the 
ability merely to perform with facility agricultural opera- 
tions, and to direct with skill the ordinary routine of his 
farm ; but that he is also desirous of knowing the rationale 
or scientific principles of all the processes he employs. We 
have no sympathy with the cant of the day with reference 
to " practical men," if by this term is understood those who 
act without reference to well-established general laws, and 
are merely guided by empirical rules or undigested expe- 
rience. However rapidly and skilfully such a person may 
perform his task, and however useful he may be within the 
limited sphere of his experience and in the practice of rules 
given by others, he is incapable of making true progress. 
His attempts at improvement are generally not only faihires, 
involving a loss of time, of labor, and of materials, but such 
as could readily have been predicted by anyone having the 
requisite amount of scientific information. It is the due 
combination of theoretical knowledge with practical skill 



86 WRITINGS OF JOSEPH HENRY. [1855-- 

which forms the most efficient and reliable character, and it 
should be the object of the agricultural collies which are 
about being established in various parts of our country to 
produce educational results of this kind. 

It is not expected that the farmer is to be a professional 
scientist, but that he should be familiar with the general 
principles of all branches of knowledge which more espe- 
cially relate to his occupation ; and the wider the extent of 
his information the better. Above all, Jie should be quali- 
fied to form a just appreciation of the value of original scien- 
tific investigations, and be ready at all times to adopt the 
principles which they may unfold, so far as they may bo 
applicable to his uses ; and moreover, be willing to render 
a due acknowledgment for the benefits thus conferred, and 
to contribute in any way in his power to the necessary, if 
not liberal, supjwrt of those who seek without the hope of 
pecuniary reward, to advance the bounds of human knowl- 
edge and of human power. The number of those in any 
age and in any country, who successfully investigate nature 
and discover new truths which form valuable contributions 
to the existing stock of knowledge, is comparatively small. 
TIic successful labor of the hands is much easier than that 
of the head; and therefore those who have actually proved 
by what they have done that they possess the ability to en- 
large the field of science should be especially cared for, and 
their energies husbanded and directed to the one pursuit to 
which they may have devoted their attention. Unfortu- 
nately however there has always been in England and this 
country a tendency to undervalue the advantages of pro- 
found thought, and to regard with favor only those investi- 
gations which are immediately applicable to the wants of 
the present hour. But it should be recollected that the 
scientific principles which at one period appear of no practi- 
cal value, and are far removed from popular appreciation, 
at a later time, in the further development of the subject, 
become the means of individual prosperity and national 
wealth. 

About fifty years ago. Sir Humphry Davy moistened a 



-1859] WRITINGS OP JOSEPH HENRY. 87 

small quantity of ordinary potash, and submitting it to the 
current of a powerful galvanic battery, observed a number 
of brilliant particles burning and exploding on the surface. 
With the intuitive perception of a highly philosophical 
mind, he saw at once in this experiment a fact of the deep- 
est significance, — the verification of a previous a priori 
hypothesis, namely, that potash and the other alkalies and 
alkaline earths were not simple substances, as they had pre- 
viously been considered, but metals compounded with oxy- 
gen. This discovery, which had an important bearing on 
the whole science of chemistry but which had no interest 
for the popular mind, has in the course of time, revolution- 
ized many of the processes of art, an(3 will furnish the means, 
in various ways, of adding to the comforts and conveniences 
of life. Within the last two years a French chemist has dis- 
covered a process of decomposing one of these alkaline 
earths, (namely, the clay which forms the basis of the soil 
of the farmer, and which hardened by flre constitutes the 
brick to build his tenement,) and of obtaining from it a metal 
as light as glass, as malleable and ductile as copper, and as 
little liable to rust as silver.* These discoveries were made 
by men whose lives were devoted to the abstract study of 
nature; they were not the results of accident, but were logical 
deductions from previous conceptions of the mind verified 
and further developed by the ingenious processes of the 
laboratory. It may be safely said, that for every one indi- 
vidual who is capable of making discoveries of this kind, 
there are at least a thousand who can apply them to useful 
purposes in the arts, and who will be stimulated to under- 
take enterprises founded upon them by the more general 
and powerful incentive of pecuniary reward. When the 
process of procuring aluminum (or the metal from clay) 
shall have been perfected, and some enterprising citizen 
shall have established a great manufactory for the production 
of the article for general use, he will confer a benefit on 
his country, be entitled to credit, and will probably re- 

* [Aluminum though first separated by Wochler in 1828, and more per- 
fectly in 1S45, was first made available by Devillo in 1855.] 



88 WRITINGS OF JOSEPH HCyRT. fUSS- 

ceive the desired remuDeration. But should the names of 
iVk chemists who originally made the discovery of the prin- 
ciples on which this public benefit depends be forgotten ? 
Ought not their labors in enlarging the bounds of knowledge 
to be properly valued, and their names held in grateful 
remembrance? If living, should they not be afforded the 
means of extending their investigations, without the distrac- 
tion of mind attendant on the efforts to obtain a precarious 
livelihood for themselves and families? 

In truth we must say — not in the way of complaint, but 
for the purpose of drawing attention to the fact and with 
the hope of somewhat changing the condition of things in 
this respect — that in no civilized country of the world is less 
encouragement given for the pursuit of abstract science than 
in the United States. The General Government has no 
power under the Constitution to directly foster pursuits of 
this kind ; and it is only by an enlightened public opinion, 
and the liberality of wealthy individuals, that a better con- 
dition of things can be hoped for. 

The great facts of the future of agriculture are to be de- 
rived from the use of the microscope, the crucible, the bal- 
ance, the galvanic battery, the polariscope, and the prism, 
and from the scientific generalizations which are deduced 
from these by the profound reflections of men who thiiik, in 
contra-distinct ion to the cflbrts of those who act. The intel- 
ligent farmer should be able (as we have already said) prop- 
erly to appreciate the value of scientific discoveries; and for 
this purpose his studies should not be confined merely to 
rules or empirical receipts, but should comprehend also the 
general princii)les on which they are founded. 

Though some of the points we shall discuss in the follow- 
ing esssay may appear at first sight to be of too abstract a 
character to be comprehended by a casual reader, yet they 
will be found on attentive perusal, to be easily understood by 
a person of ordinary intelligence. But it may be well here 
to call attention to a fact frequently overlooked, that there 
is a great difference between reading and stncbj, or between 
the indolent reception of knowledge without labor, and that 



-1859] WRITINGS OF JOSEPH HENRY. 89 

eflfort of mind which is always necessary in order to secure 
an important truth and make it fully our own. • 

Constitution of Matter. 

Laws of force and motion, — All the objects which are pre- 
sented to us in the material universe, and all the chaneres 
which we observe taking place continually among them, 
whether those which immediately surround us or those 
which we perceive at a distance, either by the naked eye or 
by means of a telescope, are referable to two principles — mat- 
ter and force. By matter, we understand the substratum 
of that which affects our senses; and by force, that which 
produces the changes which we constantly observe in the 
former. The idea of force was probably first suggested to 
us by our muscular exertions: and indeed the original 
meaning of the term is a muscle or tendon ; the Latin vis 
(force) being probably derived from the Greek *t8, or Jis. But 
we cannot imagine a force without some bodily substance by 
which, or against which it is exerted; the two ideas there- 
fore of matter and force are co-existent in the mind, and 
on a clear and definite conception of them depends that 
precise relation of the phenomena of nature denominated 
science. Though the essence of force and matter may never 
be known to us, we can study the laws by which they are 
governed, and adopt such a conception of the constitu- 
tion of matter as will enable us to generalize a vast num- 
ber of facts; to connect these with each other, or with a 
central thought; to perceive their dependencies, and thus 
in some cases; to control phenomena; to relieve the memory, 
and call into play the reasoning powers; and finally, to pre- 
dict new facts, the existence of which had never yet been 
proved by actual experience. But such a generalization 
must be based on the well-established principles of the laws 
of force and motion, and be in strict accordance with accu- 
rately ascertained facts in the various branches of physical 
inquiry, in order that it may be an exact expression of the 
apparent cause of the phenomena, and that the prediction 
from it may be true in measure as well as in mode. 



90 WRITINGS OF JOSEPn HENRY. [1855- 

The laws of force and motion, to which we have alluded 
may be expressed as follows : 

LAWS OF FORCE. 

1. Every particle of matter, at a sensible distance, attracts 
every other particle with a force varying inversely as the 
square of the distance. In the phenomena of electricity and 
magnetism, repulsion is also exhibited, acting in accordance 
with the same law. 

2. Particles of matter at insensible distances, attract and 
repel each other with great energy, the attractions and re- 
pulsions appearing to alternate with minute changes of dis- 
tance. 

LAWS OF MOTION. 

1. The law of inertia. — A body at rest tends to remain at 
rest, and when put in motion by the application of any force 
tends to move forever in a straight line with a uniform ve- 
locity. 

2. The law of the co-existence of motions. — A body impelled 
at the same moment by several forces in different directions, 
will at the end of a given time be in the same position as 
if the forces had each acted separately. 

3. Tlie law of action and re-action. — When a force acts be- 
tween two bodies of difiFerent masses, their momenta will be 
equal and opposite. 

These laws were first given to the world in a definite form 
by Sir Isaac Newton in his Principiu. They are ultimate 
facts of science, of which no satisfactory explanation is given; 
but by adopting them, as we do the axioms of geometry, 
and reasoning downward from them, all the great truths of 
modern astronomy have been evolved, as well as many of 
the facts of the molecular action of bodies. 

Atomic Theory. 

In connection with the laws of the forces and motion of 
matter, given above, we shall venture in this essay to express 
some of the widest generalizations of the present day in 
the form of what is called the atomic theory. This was the 
original conception of an imaginative Greek philosopher, 



-1859] WRITINGS OP JOSEPH HENRY. 91 

but in his mind it did not lake that definite character which 
it has since assumed under the influence of inductive science. 
It was with him the vague and indefinite product of the 
imagination, unconditioned by the actual phenomena of Na- 
ture. It was adopted by Newton, who employed it with much 
success in the different branches of his investigations; but in 
modern times it owes its greatest development and range of 
application, to Dr. John Dalton,of Manchester, England, and 
still later principally to Mr. James Joule and Professor Wil- 
liam Thomson. By means of it we are enabled to present in 
a single line a series of facts which could not otherwise be ex- 
pressed in many pages, and also to exhibit to the mind the 
connection of a series of phenomena which could not, without 
this aid, be definitely conceived. It is intimately connected 
with all branches of physical science, and (strange as it may 
appear) particularly with agriculture ; and we may therefore 
be excused for presenting it in its broadest applications, and 
with considerable detail. 

According to this theory every portion of the whole uni- 
verse, or at least that part of it which is accessible to us by 
means of the telescope, is occupied by atoms inconceivably 
minute, hard, and unchangeable, definitely separated from 
each other by attraction and repulsion. This assemblage 
of atoms constitutes the substance of the material universe; 
and to their attractions and repulsions, the forces by which 
they are actuated, is referable all the power or energy which 
produces the changes to which matter is subjected. ^ 

These atoms, thus endowed, form a plenum throughout all 
space, constituting what is called the setherial medium, and 
in it, at wide intervals from each other, are isolated masses 
of grosser matter. Which constitute our world, the planets, 
the sun, and stars. These also consist of atoms of another 
order, or of groups of atoms, with spaces between them, wide 
in comparison with the size of the atoms, which spaces are 
pervaded by the minuter atoms of the a^therial medium. 
These bodies move in the medium without encountering 
any sensible resistance. 

The various isolated bodies of the universe act upon each 



92 WRITINGS OF JOSEPH HENRY. [1859- 

other by means of the force of gravitation, and also by tre- 
mors or vibrations in this medium, radiating in every direc- 
tion from each body as a centre. 

The atoms of matter are thus separated by intervals; 
and before we proceed further it will be necessary to con- 
sider more particularly this separation. It must be recol- 
lected that the hypothesis we are presenting is not the mere 
creature of the imagination, but is based upon a generaliza- 
tion of actual observation on the different states of grosser 
matter. We shall therefore commence with the consideration 
(as an example) of the constitution of the air. This we assume 
to consist of atoms, each endowed with attracting and repel- 
ling forces. That these atoms are not in contact with each 
other, will be evident from the fact that if we apply a suffi- 
cient pressure to a quantity of air taken at its greatest known 
rarity, it may be compressed into at least one ten-thousandth 
part of its primitive volume. The sum of the magnitudes 
of the void spaces is therefore, in this case, at least ten thou- 
sand times greater than the sum of the material parts, what- 
ever be their nature. In order to explain this we are ob- 
liged to suppose that each atom is endowed with a repul- 
sive force similar to that possessed by one pole of a magnet for 
a similar pole of another magnet. And this repulsion in- 
creases with the diminution of distance between the atoms. 
It is feeble when the volume of air is expanded to its fullest 
extent, and exceedingly powerful when highly compressed. 
Whatever weight we may put on the top of a piston fitted to a 
cylinder filled with air will be sustained by the repulsion 
of the atoms. The piston will descend until each atom is 
brought precisely to that state of proximity to the next that 
the repulsive energy between the atoms just balances the 
weight on the piston, and thus the most delicate equipoise 
is afforded by the air. The slightest extraneous ibrce is suf- 
ficient to disturb the equilibrium, which is again restored by 
a scries of decreasing oscillations. 

If the atoms of the air however are removed to a much 
greater distance, the repulsion entirely ceases, and attraction 
of gravitation takes its place. If it were not for this; the 



-1859] WRITINGS OF JOSEPH HENRY. 93 

atmosphere would fly from the earth by the repulsive energy 
of its own atoms. We may therefore consider every atom 
of matter endowed with the property of obedience to the laws 
of force and motion; with inertia, by which it cannot change 
its place without the application of force, and when in motion 
cannot stop this motion without the application of an equal 
force in the opposite direction; and with attraction and re- 
pulsion, by which any two atoms placed at ever so great a dis- 
tance from each other, will tend to approach each other with 
a force increasing inversely as the square of the distance. 
When these atoms approach very near to each other they 
cease their motion, and if pressed nearer than this point 
repel each other. And it appears from experiment and 
observation that there are several alternations of attraction 
and repulsion at distances too minute however for our senses, 
and only indicated by certain phenomena. Repulsion exists 
between the atoms of the densest bodies. Platinum, for ex- 
ample, which is 21 times heavier than water, and 257,000 
times heavier than hydrogen, is still condensable. It may 
be compressed into a smaller space; and since the shrinking 
takes place equally in all directions, it follows that the atoms 
of this substance, as well as those of all gross matter, are not 
in contact. Indeed, when the hardest bodies are violently 
impelled against each other, and each is indented by the' 
other, they do not come into actual mathematical contact, 
but are mutually impressed by tlie repulsive energy, which, 
vastly increased by the diminished distance, produces the 
visible effect. 

All matter therefore is porous, whether in the gaseous, 
liquid, or solid condition. The pores may be conceived to be 
of different orders, namely, pores between the atoms, between 
the molecules or assemblages of atoms, and between the still 
larger particles. Gold itself is rendered brittle by being 
exposed to the fumes of sulphur, and solid iron is converted 
into steel by absorbing a large quantity of carbon, to which 
inter-penetration it owes its quality of hardness. 

In the case of atmospheric air and other gases the repulsive 
energy alone is exhibited in most of the mechanical phe- 



04 WRITINGS OF JOSEPH HENRY. [1855- 

noinena, while in solid bodies both the attractive and repul- 
sive are evident Thos, if we place a heavy weight on the top 
of a vertical iron bar its length will be infinitesimally dimin- 
ished. If the weight be removed, the atoms, by repulsion, 
will spring back to their original distances, and this may be 
repeated any number of times with the same result, provided 
the weight is not so great as to cause any permanent change 
which consists in a new arrangement of the atoms. If we 
now suspend the bar from one end, and apply a weight to the 
other, the bar will be minutely elongated ; and if the weight 
be removed, the atoms, by their attraction, will return to their 
normal position. In this state the atoms are at the distance 
which constitutes a neutral condition. If pushed together, 
they fly apart whenever the compressing force is removed; 
and if drawn in the direction of the length of the body, they 
are brought into the region .of attraction, and tend to bring 
the bar back to its original length when the elongating force 
is remitted. 

This constitution of matter may be represented by a series 
of balls separated from each other by helical springs. If we 
attempt to elongate this bar the springs will be drawn out 
When we attempt to compress the mass the several spires of 
the springs will be compressed closer together, and an action 
similar to repulsion will be produced. 

This repulsion of the atoms is further demonstmted by the 
elasticity of a body, or the force with which it tends to restore 
itself to its former condition when disturbed by any ejctra- 
ncous force. Tlie elasticity for instance of a rod of tempered 
steel is exhibited when we bend it It tends to return to its 
first form in obedience to two forces. The atoms on the 
convex side, after tlie rod has been bent, are slightly sepa- 
rated, and are therefore in tlie region of attraction, while those 
on the concave side are brought nearer, and thus tend to 
repel each other. If this be the c^vse, there should be a line 
somewhere near the middle of the bent rod, in which the 
atoms are neither compressed nor distended: and that such 
a neutral line does really exist can be shown by polarissed 
light, which enables us, when the experiment is made on a 



-1859] WRITINGS OF JOSEPH HENRY. 95 

rod of transparent glass, to look into the interior of the elastic 
body and observe the changes there produced. 

The difiFerence between the compressibility of air and 
of steel depends upon the difference in the repulsion of the 
atoms in the two cases. But in the latter, as well as in the 
former, there is the most delicate balance of forces ; for though 
a bar of good steel resists the weight of 60,000 pounds to the 
square inch tending to separate it in the direction of its 
length, yet the atoms may be thrown into vibration by the 
minutest force; and this is the case with all solids. A single 
tap with the end of a penknife on the table of the large lec- 
ture room of the Smithsonian Institution is sufficient not 
only to throw into vibration every particle of air in the room, 
but also every particle of the .solid parts of the edifice. The 
agitation of the air is proved by the sound, discernible in 
every part of the room, and the vibrations of the solid parts 
also by the transmission of sonorous waves with, even less 
loss than in the air. 

The repulsion of which we have spoken, and which takes 
place only at minute distances, though these may be exceed- 
ingly great when measured by the size of the atoms, appears 
to be an essential endowment of matter, and is exhibited as 
well between the atoms of the cetherial medium as between 
those of air and other grosser assemblages of matter. 

All bodies (as a general rule) arc enlarged by an increase 
of temperature. But this result, as we shall endeavor to show, 
is not from an increase of the original repulsion, but from 
an energetic vibration imparted to the atoms, which tends to 
separate them and produce the phenomena improperly as- 
cribed to an imaginary fluid called heat. 

The medium of radiation, — We are obliged to assign to the 
setherial medium a similar constitution to that possessed by 
grosser matter; namely, that it consists of inert atoms at 
great distances from each other relative to their own size, 
and each kept in position by attracting and repelling forces. 
Through this medium impulses or minute agitations are 
transmitted in celestial space, from planet to planet, and from 
system to system, which tremors or waves constitute light, 



96 WJIITINOS OF JOSEPH HENRY. [1855- 

heat, and other emanations received by us from the sun. 
That is to say, the solar emanations are not matter, but motion 
communicated from atom to atom, beginning at the lumi- 
nous body and diffused in widening spherical surfaces, en- 
larging in size and diminishing in intensity to the farthest 
conceivable portion of space. 

The atoms of the setherial medium are assumed to be 
perfectly free to move in all directions so that the earth 
and denser bodies experience no retardation as yet measur- 
able; though lighter bodies, such as comets, apparently ex- 
hibit an effect of this kind for the same reason that a flock 
of cotton is more retarded in falling through the air than 
a piece of lead. At first sight it might appear paradoxical 
that atoms, which are kept in position by powerful attraction 
and repulsion, should yet be perfectly movable among each 
other; but this condition is observed in liquid water, the 
particles of which, though they exhibit perfect mobility, yet 
repel and attract each other with immense force. This arises 
from the fact that every atom beneath the surface of a fluid 
is equally attracted and repelled on all sides by the surround- 
ing atoms, and is therefore perfectly free to move. Not so 
however with the atoms at the surface, for they are attracted 
downwards without a counteracting force to attract them 
upwards, and hence great resistance is manifested when we 
attempt to separate them. 

The author of this essay has shown from conclusive experi- 
ments that the attraction of water for water is as great as that 
of ice for ice,* and that the diflerence of the two conditions 
consists in the perfect mobility of the atoms in the former 
case, and not in the neutralization of cohesion, as is gener- 
ally supposed. If we attempt to draw up from the surface 
of water a circular disc of metal, say of an inch in diameter, 
we shall see that the water will adhere and be supported 
several lines above the general surface. This adhesion, on 
account of the perfect mobility of the atoms, is due alone to 
the attraction of the atoms of the external film and not to 
those of the whole mass which is elevated. This experi- 

[* Proceedings of American Philosophical Society. See ante^ vol. i, p. 217.] 



T; 



-1859] WRITINGS OP JOSEPH HENRY. 97 

ment, which is frequently given in elementary books as a 
measure of the feeble attraction of water for itself, is im- 
properly interpreted. It merely indicates the force of attrac- 
tion of a single film of atoms around the perpendicular 
surface, and not of the whole column elevated. The differ- 
ence then of liquidity and solidity principally consists in 
the mobility of the atoms. 

The immobility of the atoms of solids probably depends 
on their being assembled in larger groups, forming crystals, 
tissues, fibres, &c., and when force is applied to separate 
them they all resist together. In breaking a piece of steel 
for instance by extension, all the parts throughout the cross 
section of the mass simultaneously resist separation, and 
hence the great tenacity and rigidity of this substance: and 
between this and pure water other substances may be found 
having intermediate consistencies. 

We have said that the atoms of the setherial medium per- 
vade those of all other bodies, and this postulate is ana- 
logous to the inter-penetration of the particles of different 
substances between each other. 

If a piece of copper plated with silver be heated to redness 
the latter metal will be absorbed into the former. Water 
absorbs a large portion of air, and between the atoms of the 
air itself there may exist an indefinite number of other gases. 
Melted silver poured into water gives out a large portion of 
oxygen, which it had previously absorbed from the air in 
its liquid state. 

If we suppose solid bodies to be composed of a series of 
groups of atoms, the larger in succession formed from the 
smaller, the vacuity in all cases may far exceed the solidity. 

Let us now consider more minutely the nature of the 
emanations from the sun, (light, heat, &c.,) in connection 
with tfie doctrine of atoms. And in order to this we shall 
make comparisons between the phenomena of light and 
heat, and those of sound, passing by analogy from the pal- 
pable and well-known cause of familiar phenomena to that 
which is apparently not as readily accessible to our inves- 
tigations, but which when properly understood is equally 
7-2 



98 WRITINGS OF JOSEPH HENRY. [1855- 

satisfactory in the explanation, prediction, and control of 
the phenomena. 

Analogy of heat and sound, — If a heavy cannon be dis- 
charged at the distance of five or six miles, we shall see the 
flash almost instantaneously, and in about half a minute 
> after the window will bo violently agitated. 

What is the cause of this agitation? No substance shot 
from the gun has reached us, for the same effect may be per- 
ceived on all sides. The simple and true explanation of the 
phenomenon is that the atoms of air just around the mouth 
of the piece were for an instant violently pressed outwards 
by the blast of powder; these atoms were pressed against the 
next layer, and these against the next, and so on until the 
impulse reached the distant window. 

Each atom makes a short excursion or vibration, moving 
but little from its first position, and it is not therefore mat- 
ter which proceeds from the cannon and produces the dis- 
tant effect, but a propagation of motion from atom to atom. 

The atoms are endued with inertia, and time is therefore 
required, even though immense force may be applied, to 
give them full motion. And again, the atoms are not in 
contact, but are kept at a distance by repulsion, which in- 
creases when the atoms are pressed nearer each other. 
Hence the second layer of atoms does not begin to move 
with full velocity at the precise moment when motion com- 
mences in the first. 

The effect would be similar to that which would take place 
in a scries of balls kept apart from each other by helical 
springs interposed. If a blow were given to the first ball, 
so as to drive it nearer to the second, the motion would not 
be instantaneously communicated; the second would resist 
a change of state, and would not move from its position 
until the spring was considerably bent. And in this way 
time would be required to propagate motion from the first 
ball to the second, from the second to tlie third, and so on 
throughout the scries. 

If a series of lighter balls were substituted for the first, the 
springs remaining the same, it is evident the motion would 



-1859] WRITINGS OP JOSEPH HENRY. 99 

be transmitted sooner, because the inertia would be in pro- 
portion to the weighf of the balls. Hence sound is trans- 
mitted more rapidly in lighter than in heavier gases; in 
hydrogen its velocity is greater than in carbonic acid. 

Again, we may suppose the stiffness of the springs to vary, 
or in other words, the repulsion between the atoms to become 
greater or smaller. If the springs become stiffer, then it is 
evident the motion will be transmitted sooner, for if the 
springs were infinitely rigid, or what is the same if a per- 
fectly solid body were interposed between the balls, then the 
first ball could not move without at the same moment giving 
motion to the last. Hence if we increase the elasticity of a 
medium and at the same time diminish the size of its atoms 
any required velocity can be attained. Now though the 
flash is apparently perceived at the same instant at different 
places on the surface of the earth, yet we know from the 
most satisfactory evidence that this is really not the case, 
and that light and heat, as well as sound, require time for 
their propagation. Every impulse at the sun requires about 
eight minutes before it is felt at the distance of the earth. 

The analogy between light and sound does not cease here; 
and to exhibit the resemblance still further, let us suppose a 
large bell placed in mid-air to be struck a single blow 
with a heavy hammer; we know that the lower rim of metal 
will be thrown into a state of vibration; it will be com- 
pressed into an elliptical form, the shorter axis in the 
direction of the blow. The elasticity will bring it back 
to its nornial state, and will then carry it beyond in the 
other direction; and thus the part of the bell which 
is struck will continue to move backward and forward 
rapidly for a considerable time, which would be indefinitely 
prolonged were the experiment made in a perfect vacuum, 
and were no change produced in the atoms of the metal. 
In open air however the motion becomes feebler and feebler, 
and after a few minutes dies away and entirely ceases. Tlio 
principal cause of this diminution is evidently the impart- 
ing of the motion of the metal to the immediately surround- 
ing atoms of the air, and these to the next, and so on. It 



100 WRITINGS OF JOSEPH IIENUY. [1855- 

is evident that at the moment the rim of the bell is going 
from the spectator, a tendency to a vacuum would be pro- 
duced, and the atoms of the first layer of air will follow the 
metal by their elasticity, thus producing a rarefaction into 
which the atoms of the second layer of air will rush ; and 
this will advance from layer to layer until it reaches the ear 
of the observer. But before it has got far on its way, the 
side of the bell will return, and will condense the air in con- 
tact with it, and send a positive impulse in the same direc- 
tion with the first. These two impulses, travelling with equal 
velocities, and the one immediately succeeding the other, 
form an undulation. 

The effect may be strikingly illustrated by water in a long 
trough. If a small block of wood of the width of the trough 
be suddenly drawn out of the liquid at one end of the trough 
the water in immediate contact with the block will flow in 
to fill the vacuum ; the water next will flow into the space 
thus left, and so on, a hollow or negative wave will be prop- 
agated from one end of the trough to the other. If the same 
block be suddenly thrust down into the water, the effect will 
be as if a quantity of water had been suddenly added. The 
liquid will rise at the side of the block, and in its fall 
another wave will be elevated outside of it, and so on con- 
tinually, a positive wave or one of elevation, will be trans- 
mitted to the farther extremity of the reservoir. 

If the two motions of the block be made, one immediately 
succeeding the other, a compound wave or an undulation 
will be the result. The transfer in this case is again that 
of form and not of substance. The atoms of water remain 
in place, as will be evident by placing bits of wood on the 
surface; they will rise and fall, but will not advance as the 
wave passes. This is an illustration of an undulation, but 
not an exact representation of a sound wave, which consists 
in a slightly alternate backward and forward motion of each 
particle between the bell and the observer. 

An undulation of sound therefore consists of two parts — 
a condensed and a rarefied part; and hence when two series 
of undulations of the same wave length follow each other at 



-1859] WRITINGS OP JOSEPH HENRY. 101 

a distance of half an undulation, they neutralize each other, 
tlie protuberance of the one undulation exactly filling as 
it were the hollow of the other ; or to express it more accu- 
rately, the rarefied and condensed parts of the two waves 
will neutralize each other, and in this way silence may be 
produced by two intense sounds. From analogy therefore, 
if light also consists of waves, two series might be brought 
together, so as to produce darkness. Both these inferences 
are fully borne out by experiment. 

If we observe the effect of the sound waves upon a 
distant object, (such for instance as a delicate membrane 
stretched over a hoop and strewed with sand,) wo shall find 
that on sounding an instrument the sand will be violently agi- 
tated : and if the vibration is in unison with any of the strings 
of a neighboring piano, they will give forth an audible sound. 

It may be well to stop one moment to inquire in what 
this unison consists. It is well known that a string of a 
given length performs all its vibrations in the same time. 
Now if the impulses from the sounding body reach a string 
of such a time of vibration that the effect of the second im- 
pulse may be added to that of the first, or while the string 
is moving in the same direction as that given it by the first 
impulse, then the sounding will take place, or the string will 
be aroused into a motion harmonious witJi that of the sound- 
ing body. But if the impulses are not timed exactly to the 
vibrations of the string, they will meet the latter in its for- 
ward as well as in its backward movement, and thus tend 
to neutralize the effects of each other. 

In the case of light and heat, the luminous or heated body 
is supposed to be in the condition of the bell during its 
sounding. The setherial medium is the analogue of the air, 
and the vibrations of the optic nerve that of the tympanum 
of the ear. 

Further, in the case of heat, when the vibrations from 
the sun impinge upon the surfaces of solids and liquids, 
the setherial medium within the interstices of these bodies, 
and also the atoms of gross matter, are put in a state of har- 
monious vibration, and thus give rise to the phenomena 



102 WRITINGS OF JOSEPH HENRY. [1855* 

of the heat of temperature or expansion. When, as we 
have previously indicated, the vibrations of the atoms of solids 
become sufficiently violent to throw them beyond the sphere 
of cohesion, the matter is converted from a solid into an 
aeriform condition. 

But the question naturally arises. What is it that puts 
in vibration the luminous body (a candle, for instance) and 
keeps it for several hours in this constant state of agitation? 
The answer is, the continued rushing together of atom after 
atom of the carbon and hydrogen of the candle, and those 
of the oxygen of the surrounding air. An action of a 
somewhat similar kind, we must infer from analogy, is con- 
stantly producing impulses of a like character at the surface 
of the sun.. 

From the analogies of light, heat, and sound, we might 
infer, since there are different lengths of waves of the latter 
which give rise to the different notes of music; that there 
are different lengths of waves of the setherial medium pro- 
ducing different sensations in us, and different effects upon 
gross matter. And this furnishes a ready explanation of 
the well-known phenomena of the different colors of the 
spectrum, and also of the less familar but equally remark- 
able phenomena of the different kinds of radiant heat, as 
well as of the chemical and phosph erogenic emanations 
from the sun. 

That there may be different forms of waves transmitted 
through the same medium will be evident from inspecting 
the following figure, and considering the motions of the 
atoms which may be produced by a single impulse. 
h 



If we strike for example the atom a, it will be driven 
towards the second atom, and the second towards the third, 
the third towards the fourth, and so on ; the motion' will be 
transmitted along the central line of atoms to the other ex- 



-1859] WRITINGS OF JOSEPH HENRY. 103 

tremity. But while this motion takes place through the centre 
]ine of the assemblage of atoms, the motion of a will also 
bring it nearer to the atoms 6 and c, on either side ; and 
these will therefore be repelled from their positions of qui- 
escence, and lateral waves in which the atoms vibrate trans- 
versely to the direction of the ray, will be produced. It is 
probable that both kinds of vibratiop are transmitted through 
the setherial medium, and perhaps both also through the air ; 
but such is the constitution of our eyes that they can only 
perceive the results of those of the second kind, and such the 
constitution of our ears that they can only take cognizance of 
those of the first. The transverse vibration of light and 
heat was a happy conception of Dr. Thomas Young, (one of 
the discoverers of the key to the Egyptian hieroglyphics,) 
and was applied by himself and Fresnel to the explanation 
of a large and interesting series of facts classed^ under the 
name of polarization of light and heat. 

Besides the invisible emanation from the sun, which gives 
us the sensation of heat, there are others equally invisible 
which produce other effects. Indeed it is possible that there 
are an indefinite number of waves, differing in length and 
perhaps in form, though many of these must be so minute 
as to produce no appreciable physical effect at the distance 
of our planet. If a beam of light be decomposed by a prism, 
it is well known that it will be separated into parts, pro- 
ducing different colors. Now if we subject to this spectrum 
a piece of paper which has been soaked in a solution of 
nitrate of silver, we shall find that the salt of silver will be 
decomposed, and the paper will be blackened by the reduced 
metal. But the interesting part of the experiment is that 
the blackening will be more intense at a point in the pro- 
longation of the spectrum, which is entirely in the dark. 
There is then in a sunbeam, besides light and heat, a ray which 
may be separated from the former by a prism, which pro- 
duces chemical decomposition, and is hence called the chem- 
ical ray. I need scarcely remark that it is this ray, and not 
that of light, which produces the picture in the photo- 
graphic and daguerrean processes. 



104 WRITINGS OF JOSEPH HENRY. [1855- 

Again; it is well known that if we expose a diamond for 
an instant to the rays of the sun, and then convoy it to 
a dark place, we shall see it glow with a pale phosphorescent 
light; but this eflfect, long familiar as it has been to the 
natural philosopher, is now known to be the result of an 
emanation differing in some essential particulars from all 
the other emanations which we have mentioned. To prove 
this, it is sufficient to place the diamond under a plate of 
transparent mica, a substance which transmits freely light, 
heat, and the chemical emanation. This will screen the 
diamond; and the glowing, which was before very striking, 
will not now be produced. That this effect is not the re- 
sult of the absorption of a ray of light will be evident when 
we mention the fact that a diamond will glow when placed 
under a tliick plate of smoky quartz, which intercepts both 
light and chemical emanation, but freely transmits what 
is denominated the phosphorogenic ray. Tliese results are 
all in accordance, in a general way, with the constitution of 
the ffitherial medium which we have presented. 

Light and heat appear to differ only in the lengths of the 
waves, which become shorter and more intense as the tem- 
perature of the source of emanation increases ; though in 
some cases, as in that of luminous phosphorus and the light 
of the glow worm, it is emitted freely from bodies of low tem- 
perature. It is possible that light from these different sources 
may possess different physical properties. 

EkdricUy, — The phenomena of light, of heat, of the chem- 
ical and phosphorogenic emanations have all been referred 
to vibrations of the a3therial medium, and all the facts which 
have thus far been observed are in accordance with this gen- 
eralization. The question however naturally arises as to 
what explanation we can give of the multiplied and various 
phenomena constantly presenting themselves to us in con- 
nection with the changes which are taking place around 
us in nature, or which exhibit themselves to the chemist 
and physicist in their investigations of the minuter re-ac- 
tions which are brought about by their agency, and which 
are classed under the general name of electricity. It is a 



18591 WRITINGS OP JOSEPH HENRY. 105 

recognized principle of philosophy to adopt no other causes 
for the explanation of phenomena than are true and suf- 
ficient; and although the existence of the setherial medium 
may by some be doubted, yet to me it appears as certain as 
any fact can be which rests upon inferences drawn from ob- 
served phenomena. The wave motions which we refer to it, 
and which exactly agree with the observed facts, are precisely 
such as are produced in gross matter under the action of the 
laws of force and motion, and therefore we have nearly the 
same reason for believing in the existence of this diffused 
substance as in that of gross matter itself. Besides, the tend- 
ency of science is to reduce rather than increase the num- 
ber of agencies to which effects are referred as causes. We 
shall therefore assume that the setherial medium is also the 
agent by which the phenomena of electricity are produced, 
but the facts classed under the head of electricity cannot be ex- 
plained on the principle of wave-motions, and we must 
therefore seek for some other probable mechanical action 
from which they may be rationally deduced. 

Electrical phenomena may be referred to two great classes, 
statical and dynamical, or such as appear to be produced by 
the repulsive action of a fluid at rest, and by the same fluid 
in a state of motion. In some cases we have action at a 
distance on surrounding bodies which develop new and per- 
manent properties so long as the conditions remain the same; 
and in other cases effects which exactly resemble those of a 
transfer — not of a property, but of actual substance, from 
one body to the other. Now these phenomena may be re- 
ferred to an accumulation of the aetherial medium in one 
portion of space, and a corresponding diminution in the 
adjacent space. If the particles of the ©therial medium, 
when thus accumulated, act at a distance on other portions 
of the same medium we shall have a rational exposition 
of the phenomena of statical electricity; and in the restora- 
tion of the equilibrium of the medium, or in its return 
to its normal condition, we have a plausible cause of the 
dynamic efiFects belonging to the same class. But how is 
this disturbance of the equilibrium of the setherial me- 



106 WRITINGS OF JOSEPH HENRY. [1855- 

dium produced? The answer is, by the agency of gross 
matter. From the refraction of light and the various efiFects 
of heat we must infer that the setherial medium is intimately 
connected with gross matter; and although the latter may 
move in it without disturbing the equilibrium, yet when 
two pieces of gross matter are rubbed together an accumu- 
lation of the atoms of the aetherial medium may take place 
on the one and a deficiency on the other. According to this 
view there can be no electrical excitement in celestial space; 
for there gross matter does not exist, without which the 
medium cannot be coerced or the equilibrium disturbed. 
It is not supposed, in accordance with this hypothesis, that 
there is an absolute vacuum produced in the medium, but 
that a condensation exists in a given spot, and a correspond- 
ing rarefaction in the space around it. The degree of this 
condensation and rarefaction may be exceedingly slight 
in comparison with the whole elastic force of the medium, 
and therefore it is not essential to the truth of the hypothe- 
sis that any very perceptible changes should be produced in 
rays of light passing in close approximation to electrified 
bodies. 

This hypothesis is adapted to the theory of either one or 
two fluids. In the second case the setherial medium must 
be supposed to consist of two kinds of atoms, the separa- 
tion of which gives rise to the phenomena observed; and 
in the first that it consists of but one kind of atom, and 
that the eflfects observed are due to its being in excess in one 
body, and in deficiency, at the same time, in another. 

In a new investigation of the discharge of a Leyden jar, 
by the author of this essay, the facts clearly indicated the 
transfer of a fluid from the inside to the outside, and a re- 
bound back and forward several times in succession, until 
the equilibrium was attained by a series of diminishing 
oscillations. 

The magnetic phenomena may be referred to an assem- 
blage of electrical currents, according to the theory of Am- 
pere, or to a peculiar arrangement of the setherial atoms 
within the magnetic body. 



-1859] WRITINGS OP JOSEPH HENRY.' 107 

The electro-magnetic phenomena appear to be due to the 
action of the atoms of gross matter combined with that of 
the £etherial medium. 

We cannot here go into an exposition of the facts of 
electricity and magnetism, but will merely point out one 
inference from the hypothesis we have given, namely that 
electricity is not in itself a primary source of motion or 
mechanical energy, tending to produce change by a kind of 
spontaneity, (as is frequently supposed,) but is the efifect of 
a disturbance and subsequent restoration of an equilibrium, 
which disturbance has been produced by the application of 
an extraneous force. This conclusion may also be arrived 
at, without reference to the hypothesis, from the study of 
the facts themselves, which clearly demonstrate that the 
electrical equilibrium (whatever may be its nature) is never 
disturbed by its own action, but the manifestation is always 
the effect of the application of some other power, and is the 
mechanical equivalent of such disturbing cause. 

Orystalline forma, — We will now consider the grouping of 
the atoms which is intimately connected with the various 
properties of different kinds of bodies. . When the atoms of 
gross matter are suffered to approach each other, without 
disturbance or agitation, and from- an aeriform or liquid 
condition to gradually assume the solid form, they exhibit 
beautiful geometrical figures, familiarly known under the 
name of crystals. For example if a quantity of common 
salt be dissolved in water and the liquid be suffered to 
evaporate in a still place, beautiful crystals of a cubical form 
will be found in the vessel; or if ordinary saltpetre be dis- 
solved in warm water and suffered to cool, regular six-sided 
crystals will be obtained. If these crystals be reduced to 
an impalpable powder and again dissolved in hot water the 
same result will again be produced, provided the liquid be 
not in excess. 

The most interesting illustration of crystallography to 
the meteorologist is that exhibited in snow and hoar frost. 
These generally consist of stellar figures in one plane, with 
rays and branches of rays, all making angles of 60° with 



108 WRITINGS OP JOSEPH HENRY. [1855- 

each other, and under dififerent conditions of the atmosphere 
are exceedingly varied and beautiful. To explain these 
figures in a general way let us suppose three separate atoms 
to be within the sphere of mutual attraction and free to 
move; they will approach until they come within the sphere 
of repulsion, and will then evidently be found in the same 
plane at the angular points of an equilateral triangle, since 
each must be at the same distance from each of the other 
two. If a fourth atom be sufifered to approach in the same 
manner it will also arrange itself at an equal distance 
from each of the three others at the apex of a regular tri- 
angular pyramid of equal and similar faces. The next 
symmetrical arrangement which could take place would be 
in case a fifth atom were added; and if this were situated 
on the other side of the base of the pyramid a regular six- 
sided figure would result. We see from these examples 
that regular geometrical forms are the necessary effbct of 
the undisturbed grouping of the atoms, though it is impos- 
sible to deduce all the facts from considerations as simple as 
those we have given above. To adapt the hypothesis to the 
facts of the case we are obliged to assume that crystalline 
forms are not the result of the approximations of single atoms, 
but of molecules of more or less complicated structure. 

Though the exact representation of the groupings of par- 
ticles of different kinds of matter has exercised the ingenuity 
of a number of investigators, the theory is still in a very 
imperfect condition. It offers however a rich harvest for 
scientific culture, and a number of interesting conclusions 
have been deduced from the crystallographic study of bodies, 
particularly by M. Gaudin. We are obliged to suppose that 
the primary molecules which enter into crystals are them- 
selves of a geometrical shape, due to the arrangement of the 
ultimate atoms of which they are composed, and such forms 
are called the primitive forms of the crystalline molecules. 
These primitive molecules vary in form and size, as we shall 
see hereafter, and they vary also in these respects, in some 
cases of their combinations. If the two salts we mentioned in 
the commencement of this division of our subject — namely, 



-1859] WUITINGS OF JOSEPH HENKY. 109 

saltpetre and commou salt — ^be dissolved together in a suf- 
ficient quantity of water, and the liquid be suffered gradu- 
ally to evaporate, they will be found at the bottom of the 
vessel in separate crystals. The cubes of common salt can 
readily be distinguished from the long-sided prisms of salt- 
petre, and when these are chemically analyzed, each is found 
to be exclusively composed of its respective substance. Not 
a single atom of the saltpetre is found in the crystal of salt, 
nor one of the latter in the former. The same effect takes 
place if magnesia and saltpetre be dissolved in hot water and 
the solution be suffered to cool. The case however is al- 
together different when sulphate of magnesia, and sulphate 
of nickel or sulphate of zinc are crystallized together, from 
the same solution. The separation of the two substances 
does not take place as in the former instance; the individual 
crystals formed will contain both sulphate of zinc and sul- 
phate of magnesia, or sulphate of nickel and sulphate of 
magnesia, and this in every possible proportion, according 
to the relative amounts of the two salts in solution. Now if 
we compare a crystal of sulphate of magnesia with a crystal 
of sulphate of nickel, we find they have identically the same 
crystalline form: there is no perceptible difference in their 
angles, edges, or solid angles. And since a large crystal is 
built up of an aggregation of small ones of the same form, 
it is evident that the primitive molecule of sulphate of nickel 
must have the same form as that of the sulphate of mag- 
nesia; and therefore that in forming a large crystal they 
may be mingled together in the way we have just described, 
provided they are of the same size, or perhaps some multiple 
of the same size, for it is evident that it would be impossible 
to build a wall of symmetrical structure with bricks of dif- 
ferent angular forms and sizes, since the part^ would not fit 
or exactly fill the spaces. We must therefore conclude that 
though the ultimate atoms of bodies may be spherical, the 
groupings of them, which form the primitive crystallizing 
molecules, are of different geometrical shapes and sizes. 

The atomic weights or combining proportions. — Though the 
primordial atoms may all be of the same weight and size. 



110 



WRITINGS OF JOSEPH HENRY. 



[1855- 



and the different kinds of matter the result of the diflFerent 
forms in which they are grouped, 3'et in the present state of 
science there are sixty-one suhstanccs which are classed by 
the chemist as simple bodies, and which must continue thus 
to be classed until they shall be actually de-composed into 
two or more separate components. If these bodies consist of 
elementary atoms, or of groups of atoms, always of the same 
number and form, it will follow that all combinations of 
them will take place in definite and fixed proportions. Fgr 
example, it is known that one part of hydrogen by weight 
unites with eight parts of ox3'^gen to form water, and this 
liquid, whenever found, always contains the same propor- 
tion of these ingredients. But there is another compound 
of oxygen and hydrogen, of which the components are in 
the ratio of one to sixteen, and this result is precisely that 
which might have been anticipated from the theory of 
atomic combination. In the first case, if the atom of hydro- 
gen weigh one, (for instance, one millionth of a grain,) 
and the atoms of oxygen eight, (eight millionths,) then 
any amount of combination will have the same proportion. 
The combinations then will be one to eight, one to sixteen, 
and if another combination of oxygen and hydrogen exist, 
it will be in the ratio of one to twenty-four. In the first 
instance, it is one atom to one; in the next, of one atom to 
two; in the third ease, it would be one atom to three. This 
is also beautifully shown in the union of oxygen and nitro- 
gen, of which there are five difierent compounds, as exhibited 
in the accompanying table. 



Names of Compounds. 


Weight. 


Batio. 


N. 


0. 


N. 


0. 


Protoxide of nitrogen (nitrous oxide) 

Binoxide of nitrogen (nitric oxide) 

Ilyponitrous acid 

Nitrous ucid 

Nitric ucid - - -- — ---. - 


14 
14 
14 
14 
14 


8 
IG 
24 
82 
40 


1 
2 
8 

4 
6 







-1859] WRITINGS OP JOSEPH HENRY. Ill 

A glance at this table will show the justice of the remark 
of M. Dumas, that granting matter to be atomic it must 
necessarily combine as it is found to do in this instance. 
We refer to any work on chemistry for a table of atomic 
weights, and shall only give here those of the atoms which 
form the principal part of animal and vegetable bodies, 
namely, hydrogen, carbon, oxygen, and nitrogen: 

Atomic weight. 

Hydrogen ..— 1 

Carbon 6 

Oxygen 8 

Nitrogen 14 

To these, in lesser quantities, are added sulphur, 16; phos- 
phorus, 32. We may say therefore that the whole atomic 
system of animal and vegetable physiology depends princi- 
pally on the four numbers 1, 6, 7, 8. Wherever the sub- 
stances above mentioned are found in combination in anv 
of the three kingdoms of nature, they always combine ac- 
cording to these numbers, or multiples of them — a statement 
which contains in a single line a truth of the widest signifi- 
cance; which has rendered chemistry an almost mathemat- 
ical science, and its applications to agriculture an art of the 
highest value and yet of comparatively easy attain mcnt. To 
facilitate still more the use of this generalization, the atoms 
are expressed in abbreviated language. Thus water is rep- 
resented by HO — that is, one atom of hydrogen, 1, and one 
of oxygen, 8, making nine for the weight of the liquid. 
Two atoms of water would be represented by 2 HO; car- 
bonic acid by CO,, or one atom of carbon, 6, and two atoms 
of oxygen, 16; making for the atomic weight of the acid 22. 
Nitric acid is represented by NO5, and ammonia by NH3, and 
nitrate of ammonia by NO^-f NH3; indicating, in the forma- 
tion of nitric acid, five atoms of oxygen and one atom of 
nitrogen, and in that of ammonia, three atoms of hydrogen 
to one of nitrogen. The attainment of a knowledge of this 
notation is easy, while the use of it is exceedingly convenient. 

Atomic volumes. — ^The spheres of repulsion of different 
chemical atoms, or rather molecules, are probably different; 



112 WHITINGS OF JOSEPH HENRY. [1855- 

and as we may consider these spheres as constituting the sire 
of the atoms, in reference to the space which they occupy in 
combination, their magnitudes may be calculated with a 
view to ascertain whether any similarity can be found in 
the properties and action of bodies having equal atomic vol- 
umes. To explain how this may be done, let us suppose we 
wish to know the number of atoms in a given volume of 
matter of which the whole weight is known, and also the 
weight of a single atom; we shall then evidently have the 
required number of atoms by dividing the weight of the one 
atom into the weight of the whole. Now if we know the 
number of atoms in a body of given size, we can find the 
size of each atom by dividing the bulk of the whole by the 
number of atoms; but since we can only ascertain relative 
atomic weights and volumes, we suppose the volume of the 
mass to be unity, and the weight of the same to be the spe- 
cific gravity, or weight relatively to that of water. If we then 
divide the atomic weight into the specific gravity, we shall 
have the relative number of atoms; and if we divide this 
number into 1, or what is the same thing, invert the frac- 
tion and divide the atomic weight by the specific gravity, 
we shall have the relative atomic volume. We find in this 
way that there are groups of simple bodies having nearly 
the same atomic volume, and that, when crystallized in the 
same form, one may be substituted for the other, giving rise 
to compounds of similar forms, and in some cases of similar 
properties, though of different chemical constitution; and 
on the other hand, by the diflerences in the grouping of the 
same atoms bodies may be formed having entirely different 
properties. 

It frequently happens that in the union of different bodies 
in the gaseous state a condensation takes place, and the 
volume of the compound molecule is not equal to the sum 
of the volumes of atoms of wliich it is composed ; and in 
other cases the reverse effect has place, and an expansion is 
the result. 

The following table, from Faraday^s lectures,* exhibits the 

*[Thc suyect matter of a course of Six Lectures on the non-metallic 
Elements. Lect. iv. — Nitrogen; p. 206. IGmo. London. 1858.] 



-18991 



WRITINGS OP JOSEPH UENRY. 



113 



combination of volumes to illustrate this subject. In this 
the volume of nitrogen, N, is considered as unity, aAd that 
of oxygen as half unity : 

JkMe showing the grouping of elements in variotis nitrogen compounds^ and 
the difference in gwdiiy^ effected by combination, 

Ghi8, inodorous, sweet, inactive. . . [Nitrous oxide.] 
Gas, colorless, insoluble, oxidizing. . [Nitric oxide.] 

Liquid, acid, unstable [Hyponitrous acid.] 

Gas or liquid, colored, acid, soluble. [Nitrous aoid.] 
■^ Liquid, acid, colorless, corrosive. . . . [Nitric acid.] 

Gas, alkaline [Ammonia.] 

Liquid, detonating [Chloride of Nitrogen.] 

Solid, detonating [Iodide of Nitrogen.] 

Gas, combustible, odorous, poisonous. . [Cyanogen] 

One of the peculiarities of the chemical combination of 
bodies is the neutralization, in a greater or less degree, of 
their attractions. Thus sulphuric acid and quick-lime, 
which have a powerful attraction for other substances, and 
are therefore highly corrosive, when united form "plaster of 
Paris," a neutral, inert substance. An analogous result takes 
place when the north and south poles of two magnets of equal 
power are brought into contact; if they are not of equal 
power, a residual action will be left in one. In a similar 
manner two electrified glass balls, the one plus and the 
other minus, both when separate attract the surrounding 
objects; but when brought into proximity, they rush into 
contact, and neutralize one another's attraction. This fact 
distinguishes chemical attraction from the attraction of gravi- 
tation, in which there is no neutralization of this kind, and 
refers the former to that condition of the setherial medium 
called electric, in which it probaM}'' exists in strata of differ- 
ent densities around each separate molecule. The facts in 

8-2 



kH] 


"-f 


''K-2-' 


ESB 


i«h^-f^ 


JTJ H 1 R B 1 


|ir 1 a| a a 


Uhlxlx 


N C 1 C 



114 WRITINGS OF JOSEPH HENRY. [WSS- 

referonce to this point have been classed under the head of 
electro-chemistry; and in this case, as in every. other sub- 
division of our general subject, we have merely indicated a 
group of phenomena, each of which has occupied the atten- 
tion of a number of scientists, and in some cases during a 
long term of years. 

Until recently it was supposed that the physical qualities 
of bodies must depend on the nature of their elements, or 
in other words upon their chemical composition; but a great 
many substances have been discovered composed of the same 
elements in the same relative proportion and yet exhibiting 
physical and chemical properties entirely distinct one from the 
other. For example, according to Liebig, the oil of turpen- 
tine, the essence of lemon, oil of balsam of copaiba, oil of rose- 
mary, oil of juniper, and many others diflFering widely from 
each other in their odor, in their medicinal effects, in their 
boiling points, in their specific gravities, all contain the same 
elements, carbon and hydrogen, and in precisely the same 
proportion. The crystallized part of the oil of roses, a vol- 
atile solid, of which the delicious fragrance is so highly 
esteemed, is a compound body containing exactly the same 
elements and in the same proportions as the gas employed 
in lighting our streets. 

Such bodies are called isomeric (literally, of equalparts), and 
the phenomena are classed under the head of isomerism. 
These remarkable facts can only be accounted for b}' tho 
diflFerent groupings of the atoms. They exhibit as it were 
the economy of Nature in producing the most multiform 
efifects from combinations of the simplest principles, and 
almost revive in us the dreams of the alchemists relative to 
the transmutation of matter. 

Combinations of this kind are generally of a very unstable 
character and the atoms can sometimes be made to change 
their positions by an impulse from without, or by the addi- 
tion of heat, and to combine again, forming other substances 
having entirely different properties. 

The changes we have mentioned are those of bodies wKich 
are formed of groups of many chemical atoms; but a fact of 



-1859] WRITINGS OP JOSEPH HENRY. 115 

a similar character has been observed with reference to bodies 
belonging to the class which the chemist calls simple or 
elementary, because they have not as yet been decomposed. 
Of these bodies we may mention oxygen, chlorine, sulphur, 
and phosphorus. They all assume under certain conditions 
entirely diflferent properties to such an extent as almost to 
lose their identity. Oxygen, when exposed to a series of 
sparks of electricity, is converted into a substance called 
ozone, of which we shall speak more fully hereafter. Sul- 
phur, exposed to a temperature of 226° F., is melted, and if 
maintained in fusion at a temperature not exceeding 300°, 
and then suddenly thrown into water, will be found to have 
suffered no change; if however the fusion be continued 
above 300°, the material becomes black and almost solid, 
and if it now be poured into water it maintains its dark 
color, and assumes a consistence of heated glue or softened 
India rubber. In this condition its medical and other prop- 
erties are changed. Sulphur is also capable of assuming two 
different crystalline forms belonging to two primitive classes 
entirely distinct. Phosphorus undergoes a similar change, 
and chlorine, after exposure to the light, exhibits new prop- 
erties. Phenomena of this kind are classed under the head 
of aUotropism (literally, of another turn or fashion). 

Organic Molecules, 

The groups of atoms which we have thus far been con- 
sidering are principally those which have been formed 
under the influence of what is called the chemical force, and 
result from the ordinary attraction of the atoms. These are 
comparatively simple groups; but there is another class of 
groups of atoms of a much more complex character, which 
are formed of new combinations of the ordinary atoms 
under the influence, or (we may say) direction of that myste- 
rious principle called the vital force. We are able to con- 
struct a crystal of alum from its elements by combining sul- 
phur, oxygen, hydrogen, potassium, and aluminum; but 
the chemist has not yet been found who can make an atom 
of sugar from the elements of which it is composed. He can 



116 WRITINGS OF JOSEPH HENRY. [1855- 

readily decompose it into its constituents, but it is impossible 
so to arrange the atoms artificially, as in the ordinary cases 
of chemical manipulation, to produce a substance in any 
respect similar to sugar. When the attempt is made, the 
atoms arrange themselves spontaneously into a greater num- 
ber of simpler and smaller groups or molecules than is found 
in sugar, which is composed of molecules of high order, each 
containing no less than 45 atoms of carbon oxygen and 
hydrogen. 

The organic molecules, (or atoms, as they are called) are 
built up under the influence of the vital principle, from infe- 
rior groups of simple elements. These organic molecules are 
first produced in the leaves of the plant under the influence 
of light, and subsequently go through various clianges in 
connection with the vital process. After they are once formed 
in this way, they may be combined and re-combined by dif- 
ferent processes in the laboratory, and a great variety of new 
compounds artificially produced from them. 

But what is this vitiil principle which thus transcends the 
sagacity' of the chemist and produces groups of atoms of a 
complexity far exceeding his present skill? It is generally 
known under the name of the" vital /orc^"; but since the 
compounds which are produced under its influence are sub- 
ject to the same laws as those produced by the ordinary chem- 
ical forces, though differing in complexity ; and since in pass- 
ing from an unstable to a more stable condition in the form 
of smaller groups they exhibit, as will be rendered highly 
probable hereafter, an energy just equivalent to the power 
exerted by the sunbeam under whose influence they are 
produced, it is more rational to suppose that they are the 
result of the ordinary chemical forces acting under the direc- 
tion of what we prefer to call the vital principle. This is cer- 
tainly not a force, in the. ordinary acceptation of the term, or 
in that in which we confine this expression to the attractions 
and repulsions with which material atoms appear to be pri- 
marily endowed. It does not act in accordance with the re- 
stricted and uniform laws which govern the forces of inert 
matter, but with fore-thought, making provision far in ad- 



-1859] WKITINGS OP JOSEPH HENRY. 117 

vahce of a present condition for the future development of 
organs of sight, of hearing, of reproduction, and of all the 
varied parts which constitute the ingenious machinery of a 
living being. Matter without the vital influence may be 
compared in its condition to steam, which undirected is suf- 
fered to expend it^ power in producing mechanical effects on 
the air and other adjacent bodies, marked with no special 
indications of design; while matter under its influence may 
be likened to steam under the directing superintendence of 
an engineer, which is made to construct complex machinery 
and to perform other work indicative of a directing intelli- 
gence. Vitality, thus viewed, gives startling evidence of the 
immediate presence of a direct, divine, and spiritual essence, 
operating with the ordinary forces of nature, but being in 
itself entirely distinct from them. 

This view of the subject is absolutely necessary in carry- 
ing out the mechanical theory of the equivalency of heat and 
the correlation of the ordinary physical forces. Among the 
latter, vitality has no place, and it knows no subjection to the 
laws by which they are governed. 

All the constituents of organic bodies are formed of organic 
molecules, and as .we have said, are of great complexity 
and are readily disturbed and resolved into a greater nunu 
ber of lesser groups. Thus the constitution of cane sugar is 
represented by Cjj, Hja, On, making in all 45 atoms. Organic 
bodies are therefore in what may be called a state of power, 
or of tottering equilibrium, like a stone poised on a pillar, 
which the slightest jar will overturn, they are readji to rush 
into closer union with the least disturbing force. In this 
simple fact is the explanation of the whole phenomena of 
fermentation, and of the effect produced by yeast and other 
bodies, which being themselves in a state of change, over- 
turn the unstable equilibrium of the organic molecules and 
resolve them into other and more stable compounds. Fer- 
mentation then simply consists in the running down of or- 
ganic molecules from one stage to another, changing their 
constitution, and at last arriving at a neutral state. There 
is however one fact in connection with the running down of 



118 WRITINGS OP JOSEPH HENRY. [1855- 

the organic molecules which deserves particular attention, 
namely, that it must always be accompanied with the ex- 
hibition of power or energy, with a disturbance of the sethe- 
rial equilibrium in the form of heat, sometimes even of light, 
or perhaps of the chemical force, or of that of the nervous 
energy, in whatever form of motion the latter may consist. 
It is a general truth of the highest importance in the study 
of the phenomena of nature that whenever two atoms enter 
into more intimate union, heat or some form of motive 
power, is always generated. It may however be again im- 
mediately expended in effecting a change in the surround- 
ing matter, or it may be exhibited in the form of one of 
the radiant emanations. 

Balance of Nature. — The term balance of organic nature 
was first applied, we think, by Dumas to express the rela- 
tions between matter forming animals and vegetables, and 
the same matter in an inert condition. We shall apply the 
term "balance of nature" in a more extended sense, and in- 
clude within it the balance of power, as well as the trans- 
formations of matter. The amount of matter in the visible 
universe is supposed to remain the same, though it is subject 
to various transformations, and appears under various forms, 
— now builtupinto organic molecules, and now again resolved 
into the simple inorganic compounds. The carbon and other 
materials absorbed from the air by the plant is given back to 
the atmosphere by the decaying organisms, and thus w^hat 
may be called a constant balance is preserved. But this 
balance*(if we may so call it) does not alone pertain to the 
matter, but also to the energy which is employed in produc- 
ing these changes. It may disappear for a while, or may 
be locked up in the plant or the animal, but is again des- 
tined to appear in another form and to exert its effects per- 
haps in distant parts of celestial space. 

To give precision to our thoughts on this subject let us 
suppose that all the vegetable and animal matter which now 
forms a thin pellicle at the surface of the earth were removed 
— that nothing remained but the germs of future organisms 
buried in the soil and ready to be developed when the proper 



-1859] WRITIKOS OP JOSEPH HENRY. 119 

influences were brought to bear upon them. Let us further 
suppose the sun to cease giving emanations of any kind into 
space. The radiation from the earth, uncompensated by 
impulses from the sun, would soon reduce the -temperature 
of every part of the surface to at least 60° below-zero ; all the 
matter and liquid substances capable of being frozen would 
be reduced to a solid state ; the air would cease to move, and 
universal stillness and silence would prevail. 

Let us now suppose that the sun were to give forth rays 
of heat alone; these would radiate in every direction from 
the celestial orb, and an exceedingly small portion of them, 
in comparison with the whole, would impinge against the 
surface of our distant planet, would melt the ice first on the 
equator, then on the more northern and southern parts of 
the globe, and finally their genial influence would be felt 
at the poles. The air would be unequally rarefied in the 
different zones, the winds would again be called forth, vapor 
would rise from the ocean, clouds would be formed, rain 
would descend, and storms and tempests would resume their 
sway. 

^ If the sun should again intermit its radiation all these 
motions would gradually diminish and after a time entirely 
cease; the heat given to the earth would in part be retained 
for awhile, but in time would be expended ; the water would 
slowly give out its latent heat and be again converted into 
ice. Something of this kind takes place in the northern and 
southern parts of the earth during the different periods of 
summer and winter. Since the mean temperature of the 
earth does not vary from year to year, it follows that all the 
excess of heat of summer received from the sun is given off 
in winter, and hence the impulses from this luminary which 
constitute all the energy producing the changes on the sur- 
face of the earth, merely lingering awhile, are again sent 
forth into celestial space, changed it may be in form, but 
not in the amount of their power. The solar vibrations have 
lost none of their energy, for the water has returned to the 
state of ice, and the surface of the earth is again in the same 
condition in which it was before it received the solar impulse. 



120 WRITINGS OP JOSEPH HENRY. [1855^ 

The energy of the solar vibrations communicated to the ice 
modifies its cohesion, converting it into the liquid state^ 
and the ice again becoming solid gives out the same amount 
of heat in a less energetic form. Even the motive power of 
the wind is expended by the friction of its particles in pro- 
ducing a portion of the heat which gave rise to its motion, 
and this also is radiated into celestial space. 

But the most interesting part of our inquiry relates to 
the effects which the radiation alone of heat from the sun 
would have on the vegetable gejms buried in the soil. If 
these germs were enclosed in sacs filled with starch and other 
organic ingredients, stored away for the future use of the 
young plant, as in the case of the tuber of the potato, or the 
fleshy part of the bean, as soon as the sun penetrated beneath 
the surface in sufficient degree to give mobility to the com-- 
plex organic molecules of which these materials consist, (the 
proper degree of moisture also supposed to be present,) ger- 
mination would commence. The young plant would begin 
to be developed, would strike a rootlet downward into the 
earth, and elevate a stem towards the surface furnished with 
incipient leaves: The growth would continue until all the 
organic matter in the tuber or sac was exhausted; the fur- 
ther development of the plant would then cease, and in a 
short time decay would commence. 

But let us dwell a few minutes longer on the condition of 
the plant and the tuber before the downward action becomes 
the subject of consideration. If we examine the condition of 
the potato which was buried in the earth, we shall find re- 
maining of it nothing but the skin, which will probably con- 
tain a portion of water. What has become of the starch and 
other matter which originally filled this large sac? If we 
examine the soil which surrounded the potato, we do not 
find that the starch has been absorbed by it ; and the answer 
which will, therefore naturally be suggested is, that it has 
been transformed unto the material of the new plant, and it 
was for this purpose originally stored away. But this, 
though in part correct, is not the whole truth; for if we 
weigh a potiito prior to germination, and weigh the young 



-1859] WRJTINOS OP JOSEPH HEITRY. 121 

plant afterward we shall find that the amount of organic 
matter contained in the latter is but a fraction of that which 
was originally contained in the former. We can account in 
this way for the disappearance of a part of the contents of 
the sac, which has evidently formed the pabulum of the 
young plant. But here we may stop to ask another ques- 
tion: By what power was the young plant built up of the 
molecules of starch? The answer would probably be, by the 
exertion of the vital force; but we have endeavored to show 
that vitality is a directing principlcy and not a mechanical 
power, the expenditure of which does work. The conclusion 
fb which we would arrive will probably now be anticipated. 
The portion of the organic molecules of the starch, &c., of 
the tuber, as yet unaccounted for, has run down into inor- 
ganic matter, or has entered again into combination with 
the oxygen of the air, and in this running down, and union 
with the oxygen, has evolved the power necessary to the 
organization of the new plant. 

If we examine the skin of a potato, we shall find it perfo- 
rated by innumerable holes, through which the oxygen 
penetrates into the interior to enter into combination with 
the starch, (or in other words, to burn it by a slow combus- 
tion,) and through which the carbonic acid and vapor of water 
again find their way into the atmosphere. We see from this 
view that the starch and nitrogenous materials, in which 
the germs of plants are imbedded, have two functions to 
fulfil; the one to supply the pabulum of the new plant, and 
the other to furnish the power by which the transformation 
is effected, the latter being as essential as the former. In 
t"he erection of a house, tlie application of mechanical power 
is required as much as a supply of ponderable materials. 

But to return to our first supposition. We have said (and 
the assertion is in accordance with accurate observation) that 
the plant would cease to increase in weight under the mere 
influence of heat, however long continued, after the tuber 
was exhausted. Some slight changes might indeed take 
place; a small portion of pabulum might be absorbed from 
the earth ; or one part of the plant might commence to decay. 



i 



122 WRITINGS OF JOSEPH HENRY. [1855- 

and thus furnish nourishmeut to the remaining parts; but 
changes of this kind would bo minute, and the plant, under 
the influence of heat alone, would in a short time cease to 
exist. 

Let us next suppose the sun to commence emitting rays 
of light, in addition to those of heat. These, impinging 
against the earth, would probably produce some effects of a 
physical character; but what these effects would be we are 
unable, at the present time, fully to say. We infer however 
that the light, not immediately reflected into space, would 
be annihilated ; but this could not take place without com- 
municating motion to other matter. It would probably be 
transformed into waves of heat of feeble intensity. 

Let us now suppose, in addition to heat and light, the 
chemical rays to be sent forth from the sun. These would 
also produce various physical changes, the most remarkable 
of which would bo in regard to the plant. 

The carbonic acid of the atmosphere, in contact with the 
expanding surface of the young leaves, would be absorbed 
by the water in their pores, and in this condition would be 
decomposed by the vibrating impulses which constitute the 
chemical emanation. The atoms of carbon and oxygen, of 
which the carbonic acid is composed, would be forcibly sepa- 
rated ; the atoms of oxygen would be liberated in the form 
of gas, and the carbon be absorbed to build up, under the 
directing influence of vitality, the woody structure of the 
plant. In this condition the pabulum of the plant is prin- 
cipally furnished by the carbonic acid of the air, while the 
impulses of the chemical ray furnish the primary power by 
which the de-composition and the other changes are effected. 
This is the general form of the process, leaving out of view 
minute changes, actions, and re-actions, which m ust take place 
in the course of organization. 

All the material of which a tree is built up, (with the ex- 
ception of that comparatively small portion which remains 
after it has been burnt, and constitutes the ash,) is derived 
from the atmosphere. That this is so can be proved by 
growing a plant in perfectly pure flint sand, to which a 



-18591 WRITINGS OP JOSEPH HENRY. 123 

minute quantity of foreign substance is added, and sprink- 
ling with distilled water. In this case the plant will yield 
the usual amount of carbon or charcoal, although there was 
none in the soil in which it grew. 

In the decomposition of the carbonic acid by the chemical 
ray a definite amount of power is expended, and this re- 
mains (as it were) locked up in the plant so long as it con- 
tinues to grow; but when it has reached its term of months 
or years, and some condition has been introduced which 
interferes with the balance of forces, then a reverse process 
commences, the plant begins to decay, the complex organic 
molecules begin* to run down into simpler groups, and then 
again into carbonic acid and water. The materials of the 
plant fall back into the same combinations from which they 
were originally drawn, and the solid carbon is returned in 
the form of a gas to the atmosphere whence it was taken. 
Now the power which is given out in the whole descent is, 
according to the dynamic theory, just equivalent to the 
power expended by the impulse from the sun in elevatingi* 
the atoms to the unstable condition of the organic molecules. 
If this power is given out in the form of vibrations of the 
setherial medium constituting heat it will not be appreciable 
in the ordinary decay — say of a tree, extending as it may 
through several years; but if the process be rapid, as in the 
case of combustion of wood, then the same amount of power 
will be given out in the energetic form of heat of high in- 
tensity. This heat will again radiate from the earth, and 
in this case, as in that we have previously considered, the 
impulse from the sun merely lingers for a while upon the 
earth, and is then given back to celestial space changed in 
form, but undiminished in quantity. It may continue its 
radiating course through stellar space until it meets planets 
of other systems; but to attempt to trace it further would be 
to transcend the limits of inductive reason, and to enter 
those of unbridled fancy. 

In the process we have described, the carbon, hydrogen, 
and other substances which are absorbed from the atmos- 
phere are returned to this great reservoir to be used again, 



124 WRITINGS OP JOSEPH HENRY. [1855- 

and it may be to undergo the same changes many times in 
succession. The earthy materials are again returned to the 
earth, and all the conditions, as far as the individual plant 
which we are considering is concerned, are the same as they 
were at the beginning. The absorption of power in the de- 
composition of the carbonic acid gas, and its evolution again 
when the re-composition is produced of the same atoms, is 
precisely analogous to that which takes place in forcibly 
separating the poles of two magnets, retaining them apart 
for a certain time, and suffering them to return by their 
attractive force to their former union. The energy developed 
in the approach of the magnets towards each other is just 
equal to the force expended in their separation. 

By extending this reasoning to the vast beds of coal which 
are stored away in the earth, we are brought irresistibly to 
the conclusion that the power which is evolved in the com- 
bustion of this material, now so valuable an agent in the pro- 
cesses of manufacture and locomotion, is merely the equiv- 
iilent of the force which was expended in de-composing the 
carbonic acid which furnished the carbon of the primeval 
forests of the globe; and that the power thus stored away 
millions of years before the existence of man, like other pre- 
ordinations of Divine Intelligence, is now employed in 
adding to the comforts and advancing the physical and in- 
tellectual well-being of our race. 

In the germination of the plant a part of the organized 
molecules runs down into carbonic acid to furnish power for 
the new arrangement of the other portion. In this process 
no extraneous force is required: the seed contains within 
itself the power and the material for the growth of the new 
plant up to a certain stage of its development. Germination 
can therefore be carried on in the dark, and indeed the 
chemical ray which accompanies light retards rather than 
accelerates the process. Its office is to separate the atoms of 
carbon from those of oxygen in the decomposition of the car- 
bonic acid, while that of the power w^ithin the plant results 
from the combination of these same elements. The forces 
are therefore antagonistic, and hence germination is more 



-1859] WIUTIKGS OF JOSEPU UENRY. 125 

rapid when light is excluded; an inference borne out by 
actual experiment. 

Animal Organism, 

Besides plants, there is another great class of organized 
beings, viz: animals; and as we commenced with the con- 
sideration of the seed in the first case, let us begin in this 
with the egg. This (as is well known) consists of a sac or 
shell containing a mass of organized molecules formed of 
the same elements of which the plant is composed, viz: car- 
bon, hydrogen, oxygen, and nitrogen, with a minute portion 
of sulphur and other substances. Indeed this material is 
derived exclusively from the animal kingdom. Without 
attempting to describe the various transformations which 
take place among these organized molecules, a task which 
far transcends our knowledge or even that of the science of 
the day, we shall merely consider the general changes which 
occur of a physical character. 

As in the case of the seed of the plant, we presume that* 
the germ of the future animal pre-exists in the egg, and that 
by subjecting the mass to a degree of temperature suflBcient 
perhaps to give greater mobility to the molecules, a process 
similar in its general eflFect to that of the germination of the 
seed commences. Oxygen is absorbed through some of the 
minute holes in the shell, and carbonic acid constantly ex- 
haled from others. A portion then of the organic molecules 
begins to run down, and is converted into carbonic acid and, 
possibly, water. During this process power is evolved within 
the shell, — wo cannot say, in the present state of science 
under what particular form ; but we are irresistibly con- 
strained to believe that it is expended under the direction 
again, of the vital principle, in re-arranging the organic 
molecules, in building up the complex machinery of the 
future animal, or developing a still higher organization, con- 
nected with which are the mysterious manifestations of 
thought and volition. 

In this case, as in that of the potato, the young animal as 
it escapes from the shell weighs loss than the material of the 



126 WRITINGS OF JOSEPH HENRY. [1855- 

egg previous to the process of incubation. The lost material 
in this case as in the other has run down into an inorganic 
condition by combining with oxygen, and in its descent has 
developed the power to effect the transformation we have 
just described. 

We have seen in the case of the young plant that after it 
escapes from the seed and expands its leaves to the air^ it 
receives the means of its future growth principally from the 
carbon derived from the de-composition of the carbonic acid 
of the atmosphere, and its power to effect all its changes 
from the direct vibratory impulses of the sun. The young 
animal however is in an entirely different condition; ex- 
posure to the light of the sun is not necessary to its growth 
or existence; the chemical ray by impinging on the surface 
of its body does not de-compose the carbonic acid which may 
surround it, the conditions necessary for this de-composition 
not being present. It has no means by itself to elaborate 
organic molecules, and is indebted for these entirely to its 
food. It is necessary therefore that it should be supplied 
with food consisting of organized materials, that is of com- 
plex molecules in a state of instable equilibrium, or of power. 
These molecules have two offices to perform, one portion of 
them, by their transformations, is expended in building up 
the body of the animal, and the other in furnishing the 
power rec^uired to produce these transformations, and also in 
furnishing the energy constantly expended in the breathing, 
the pulsations, and the various other mechanical motions of 
the living animal. We may infer from this that the animal 
in proportion to its weight before it has acquired its growth 
will require more food than the adult unless all its volun- 
tary motions be prevented; and secondly, that more food 
will be required for sustaining and renewing the body when 
the animal is suflFered to expend its muscular energy in 
labor or other active exercise. 

The power of the living animal is immediately . derived 
from the running down of the complex organized molecules 
of which the body is formed, into their ultimate combination 
with oxygen in the form of carbon, water, and ammonia. 



-1859] WRITINGS OF JOSEPH HENEY. 127 

Hence oxygen is constantly drawn into the lungs, and car- 
bon is constantly evolved. In the adult animal when a 
dynamic equilibrium has been attained the nourishment 
which is absorbed into the system is entirely expended in 
producing the power to carry on the various functions of life, 
and to supply the energy necessary to perform all the acts 
pertaining to a living, sentient, and it may be, thinking be- 
ing. In this case, as in that of the plant, the power may be 
traced back to the original impulse from the sun, which is 
retained through a second stage, and finally given back 
again to celestial space, whence it emanated. All animals 
are constantly radiating heat, though in different degrees, 
the amount in all cases being in proportion to the oxygen 
inhaled and the carbon exhaled. The animal is a curiously 
contrived arrangement for burning carbon and hydrogen, 
and the evolution and application of power. In this respect 
it is precisely analogous to the locomotive, the carbon burnt 
in the food and in the wood performing the same office in 
each. The fact has long been established that power cannot 
be generated by any combination of machinery. A machine 
is an instrument for the application of power, and not for 
its creation. The animal body is a structure of this char- 
acter. It is admirably contrived, when we consider all the 
offices it has to perform, for the purpose to which it is 
applied, but it can do nothing without power, and that, as 
in the case of the locomotive, must be supplied from with- 
out. Nay more, a comparison has been made between the 
work which can be done by burning a given amount of car- 
bon in the machine, man, and an equal amount in the ma- 
chine, locomotive. The result derived from an analysis of 
the food in one case and the weight of the fuel in the other, 
and these compared with the quantity of water raised by 
each to a known elevation, gives the relative working value 
of the two machines. From this comparison, made from 
experiments on soldiers in Germany and France, it is found 
that the human machine, in consuming the same amount 
of carbon, does four and a half times the amount of work of 
the best Cornish engine. The body has been called " the 



128 WHITINGS OF JOSEPH HENRY. [1855- 

house we live in," but it may be more truly denominated 
the machine we employ, which furnished with power and 
all the appliances for its use, enables us to execute the in- 
tentions of our infelligence, to gratify our moral natures, 
and to commune with our fellow beings. 

This view of the nature of the body is the furthest re- 
moved possible from materialism; it requires a separate 
thinking principle. To illustrate this, let us suppose a loco- 
motive engine equipped with steam, water, fuel, — in short, 
with the potential energy necessary to the exhibition of im- 
mense mechanical power; the whole remains in a state of 
dynamic equilibrium, without motion or sign of life or in- 
telligence. Let the engineer now open a valve which is so 
poised as to move with the slightest touch, and almost by mere 
volition, to let on the power to the piston; the machine now 
awakes, as it were, into life. It rushes forward with tremen- 
dous power, it stops instantly, it returns again, it may be at 
the command of the master of the train ; in short, it exhibits 
signs of life and intelligence. Its power is now controlled 
by mind — it has, as it were, a soul within it. The engine 
may be considered as an appendage or a further develop- 
ment of the body of the engineer, in which the boiler and 
the furnace arc an additional capacious stomach for the evo- 
lution of the power; and the wheels, the cranks and levers, 
the bones, the sinews, and the muscles by which this power 
is applied. 

There is however one striking diflference between the ani- 
mal body and the locomotive machine which deserves our 
special attention, namely, the power in the body is constantly 
evolved by burning (as it were) parts of the materials of the 
machine itself, as if the frame and other portions of the 
wood-work of the locomotive were burnt to produce the 
power, and then immediately renewed. The voluntary mo- 
tion of our organs of speech, of our hands, of our feet, and 
of every muscle in the body is produced, not at the expense 
of the soul, but at that of the material of the body itselt 
Every motion manifesting life in the individual is the result 
of power derived from the death (so to speak) of a part of his 



^1859] WBITINGS OP JOSEPH HENRY. 120 

body. We are thus constantly renewed and constantly con- 
sumed, and in this consumption and renewal consists animal 
life. When the proper balance between these two processes 
is destroyed the derangement and death of the body ensue. 
The rational, directing, thinking, willing soul, analogous 
to that Divine intelligence manifested in all the works of 
Nature, dissolves its connection with matter, and finds in 
another, and perhaps successive conditions, an immortal 
existence. 

In this great perpetual circle of change nothing is lost. 
The earthy matter absorbed by the roots of the plant is 
given back to the earth in the ejectments and decay of the 
animal body; the carbon, the hydrogen, the nitrogen, are 
returned to the air whence they were drawn; the solar im- 
pulses by which all the transformations were effected, are 
restored unaltered in quantity to the celestial space; and in 
the case of man, the soul, fraught with the moral eflFects of 
its connection with matter, returns to its Divine Creator, the 
source of all power, moral, intellectual, and physical. 

• 

Mechanical Energy. 

The last remarks will lead us naturally to the subject of 
mechanical energy and the correlation of physical forces, a 
comparatively new class of ideas, which is at present occupy- 
ing the attention of some of tlie first men of Europe and this 
country. Indeed, one reason which has induced us to adopt 
the atomic theory in this essay is, that we miglit give the 
clearest and simplest view of these new and interesting ideas, 
as well as some of the deductions which have been made 
from them. The fact has been long conclusively established 
in the minds of scientific men, that matter cannot be anni- 
hilated, except by the almighty fiat of Him who called it 
into existence; and the idea has been lately adopted, that 
the natural forces associated with matter, namely, the attrac- 
tions and repulsions, are also as indestructible as the matter 
itself; moreover, the tendency of scientific speculation at the 
present day is to the conclusion that all energy, as it is 
calledi or Uiat which produces the changes in the material 
9-2 



130 WRITINGS OF JOSEPH HENRY. [1855- 

universe, is due to the movements produced by attraction 
and repulsion of the atoms in passing from a primordial 
state of instability to one of final stability or relative rest. 
It must be evident to any person who is acquainted with the 
simplest principles of mechanics, that in a universe in which 
all the atoms are in equilibrium, or have approached each 
other as nearly as possible, there can be no spontaneous 
motion. Such a universe must ever remain, in all its parts, 
a dead, inert, and lifeless mass. It can only be awakened 
to life and motion by the application of power from without. 
Mechanical energy is only exhibited while two atoms are 
rushing together; when they have united in combination, 
they exhibit an apparent neutralization of all power to pro- 
duce change in themselves or other bodies. 

" Fill," says Professor Faraday, " an India-rubber bag with a 
mixture of oxygen and hydrogen in the proportion of 8 parts 
to 1 by weight; and blowing with it a number of soap-bubbles 
in a large dish, apply a lighted taper to the bubbles and 
observe the result. It is a violent deafening explosion, at- 
tended with the evolution of light and heat, giving evidence 
of tremendous power. But now we come to the result of 
this explosion, which is water — nothing but water. To 
me the whole range of natural phenomena does not pre- 
sent a more wonderful result than this. Well known, and 
familiar though it be, a fact standing on the very threshold 
of chemistry, it is one over which I ponder again and again 
with wonder and admiration. To think that these two vio- 
lent elements, holding in their admixed parts such energ)'', 
should wait until some disturbance is effected, and then rush 
furiously into combination, and form the bland and un-irri- 
tating liquid water, is to me, I confess, a phenomenon which 
awakens new feelings of wonder as often as I view it."* 

Wonderful as this may appear, it is but a simple illustra- 
tion of a general law. The power exhibited was in the mo- 
mentum produced by the energetic action of the two atoms 
on each other, and the consequent high velocity with which 
they rushed into union. The noise produced was due to the 
intense agitation given to the air; the light and heat to the 

♦[Faraday's Six Lectures on the non-metallic Elements.' Lect. iii, pp. 
175, 17G.] 



-1859] WRITINGS OP JOSEPH HENRY. 131 

agitation of the aetherial medium ; and these together are 
equal to the energy generated by the reciprocal motion of 
the atoms. If by any means a force were applied to separate 
the atoms to the same distance at which they were at first, 
this force would be just equal to that due to the rushing 
together of the atoms. Two atoms separated, and in a con- 
dition to be violently drawn together, are said to be in a 
state of energy or power ; but when they have entered into 
combination, they are then in a state of inertness. The 
same may be said of a weight elevated above the surface of 
the earth. A certain amount of muscular power must be 
exerted to overcome the attraction of gravitation, and to raise 
the weight to the given height, say ten feet. It is then in a 
state of power, or in a condition to produce permanent 
changes in matter, and other effects which we technically 
denominate " work." 

The energy developed in the weight may be employed to 
drive a pile into the ground, or it may be made to turn a mill 
and grind corn ; but the work done in these two cases, when 
properly measured, will be the same, and just equal to that 
expended in elevating the weight. If the weight be raised 
to double the height, twice the force will be expended in ac- 
complishing this effect, and the weight in its descent to the 
earth will also do a corresponding amount of work. The 
explanation of the development of the energy exhibited in the 
fall of a body from a height will be plain when we consider 
that gravity acts on the mass with a force proportioned to 
the number of pounds in weight at every point in its des- 
cent; and if we suppose that in the first this attraction gave 
it a certain velocity, and gravity were then to cease, the body, 
on account of its inertia, would continue to descend with 
this velocity to the end of its course. But if the attraction 
continues to act, new impulses are imparted at every instant, 
and the velocity will continually increase until it reaches the 
ground, where it will produce an effect which is the equiva- 
lent of the power accumulated in its descent. The mechan- 
ical energy of matter therefore is measured by the distance 
of the atoms into the intensity of the attraction at the differ- 



132 WRITINGS OF JOSEPH HENRY. [1865- 

ent points of their path of approach. If the atoms of any 
part of the material universe are in the condition of the atoms 
of oxygen and hydrogen after they have united to form 
water — that is, in the closest approximation and a complete 
neutralization of their affinities — the matter in this portion 
of space will be entirely inert, and unless disturbed by ex- 
traneous force, no change can take place among its parts. 
Matter wanting that peculiar characteristic which eminently 
distinguishes mind, namely, spontaneity of action, all will 
be in perfect quiescence. 

From the researches of the geologist, the chemist, and the 
physicist, we are enabled to assert that such is the condition 
of our earth and its attendant satellite. All the chemical 
elements which are found in the crust of the globe have 
gone into a state of permanent quiescence. The metals and 
oxygen have united to form oxides, and these with the 
acids to form other stable compounds ; and were it not for 
the disturbing influence of the impulses from the sun, the 
present system of continued change, of growth and decay, 
of storms and of calms, would cease, and the whole surface 
of our planet would exhibit a dreary desolation of darkness 
and stillness, of silence and death. Indeed as it is, the 
changes and ever- varying phenomena in which we are so 
much interested, and a knowledge of which constitutes the 
highest earthly wisdom, arc confined to an almost infinitesi- 
mal pellicle at the surAxce of the earth. Organic matter is 
found but a few feet below the surface of the soil, and plants 
cannot exist in the ocean beyond the depth to which the 
rays of the sun penetrate. But this state of things has not 
always existed. It is conclusively proved by the past his- 
tory of the globe, as written upon the rocks which form its 
outer strata, that its atoms were once in a state of intense 
agitation, or in other words, that the globe was in a con- 
dition of high temperature, and that the vibrations have 
been imparted to the surrounding ajtherial medium and 
and thus radiated off into space. We arrive at this conclu- 
sion, not only from an examination of the condition of the 
strata, but from the fact that wherever we penetrate beneath 






-1859] WRITINGS OF JOSEPH HENRY. 133 

the surface, beyond the depth of the influence of external 
climate, the temperature uniformly increases at the rate of 
about 1® F. for every 50 feet. Our globe then consists of a 
mass of matter which has been gradually cooled from a state 
of intense heat, and at its surface has arrived at a con- 
dition of equilibrium, the heat which its surface gives off* 
into space being just compensated by that received from the 
sun. The permanency of our temperature therefore depends 
upon that of the great' central luminary of our system itself. 
But whether 

'* The sun himself shall fade, and ancient night 
Again involve a desolate abyss/' 

must be left for future consideration. 

The ideas which are here given had their origin in the 
attempts which were made to produce self-moving machines. 
The possibility of such contrivances appeared to be sanctioned 
by the apparently spontaneous motion of men and lower 
animals. The idea that these motions were the results of 
the chemical action of food had not yet entered the mind; 
and it was only after many fruitless attempts, and the ex- 
penditure of much thought, time, and labor that the con- 
clusion was at length arrived at that a machine is a mere 
instrument for the application and modification of power or 
energy, and that in no case can it do more work or produce 
more changes in matter, or in other words, it can break 
apart no more atoms than are equivalent to the power which 
has been applied to it. The same amount of power which 
we apply at one extremity of a machine, properly estimated, 
is equal to the sum of the resistances at the other, and the 
two precisely balance each other. From considerations of 
this kind we arrived at the conception of the correlation of 
the physical forces and the re-conversion of the equivalent 
of one into that of the other. 

We may do the same work by heat properly applied, or 
by a fall of water, or by muscular energy. For example, a 
disc of iron may be made to revolve rapidly with a mill 
driven by a fall of water, and if this is allowed to rub with 
some pressure against another iron plate a great amount of 



134 WRITINGS OF JOSEPH HENRY. [1855- 

friction will be produced ; the mechanical collision of the 
surfaces will set the atoms of the plates in that state of vibra- 
tion which constitutes heat, and which, if unobstructed, will 
be communicated to the surrounding setherial medium and 
radiated to adjacent bodies or oflF into celestial space. But 
if detained and applied it may be used to produce changes 
in matter, such as the boiling of water, the driving of a steam 
engine, and other objects. Now, if it were possible to collect 
and concentrate all the impulses of the heat vibrations, and 
apply them without loss by means of a machine to the eleva- 
tion of water, the quantity thus raised and the height to 
which it is raised would be precisely equal to the height and 
quantity of water, the fall of which produced the first effect. 
Similarly, if by a steam engine we put in motion the plate 
of a large electrical machine and disturb the equilibrum of 
the aether, condensing a portion of it in one part of space and 
rarefying it in another portion, the force which would be 
exerted in the restoration of the equilibrium, or in the elec- 
trical discharge, would be just equal to the amount of energy 
exerted in producing the coerced condition. If in this case 
the coerced equilibrium is retained for a day, a year, or a 
century, so long the amount of energy expended to produce 
it will, as it were, be locked up but not lost. It will be ready 
to appear and do work as soon as the detent which prevents 
the commencement of motion is removed. As a further ex- 
ample of this, suppose a heavy weight to be elevated by steam 
power to the top of a high pillar, and there placed on an 
equipoise, so that the least force applied may overturn it 
and enable it to commence its fall. In its descent it will 
receive at every instant a new impulse from gravity, and 
when it arrives at the ground it will expend its accumulated 
energy in penetrating the surface and in the production of 
heat, sound, and tremors of the earth. When the weight is 
resting on the top of the pillar, ready to fall off with the 
slightest touch, it is said to be in a state of potential energy; 
and when it has almost reached the earth and is moving 
with the full velocity of the fall, it has converted its potential 
energy into actual pj)wer. 



-1859] WRITINGS OF JOSEPH HEKRY. 135 

The general conclusion whicli has been arrived at is that 
the diflFerent physical energies — wliether called chemical 
action, heat, light, electricity, magnetism, muscular mo- 
tion, or mechanical power, are all referable to the disturbance 
of the equilibrium of the atoms and the subsequent resto- 
ration due to their attractions and repulsions; and that all 
these forms of energy are in one sense convertible into each 
other, or in other words the force generated in the restora- 
tion of the equilibrium in one case is suflBcient to disturb it, 
though in a diflFerent form perhaps, in another. We must 
guard against the erroneous idea which some have incon- 
siderately adopted, that one form of power can be actually 
converted into another, as heat into electricity, or the con- 
verse. The theory of energy merely declares that the 
power exhibited in the electrical discharge is the equiva- 
lent of the muscular energy expended in charging the 
battery, and not that muscular energy is converted into 
electricity. 

The origin of heat produced by friction for a long time 
perplexed the most sagacious.philosophers. Our celebrated 
and ingenious countryman, Count Rumford, caused a quan- 
tity of water .to boil for several hours by the heat generated 
in boring a cannon; and after the process was ended, he 
found that the borings and the cannon contained as much 
heat as at the commencement of the experiment. From 
this result he boldly proclaimed -that heat was not matter, 
but the vibrations of the atoms of matter, and that in his 
experiment the heat was generated by the friction of the 
drill on the metal. 

Later researches have constantly tended to strengthen 
the probability of this view, and even to establish the gen- 
eral fact, that when mechanical power is produced by the 
expenditure of heat, a quantity of heat disappears, bearing 
a fixed proportion to the power produced ; and conversely, 
that when heat is produced by the expenditure of mechani- 
cal power, the quantity of heat produced bears a fixed pro- 
portion to the power expended. Thus in the case of a 
steam engine doing no work, the quantity of heat given 



136 WRITINGS OF JOSEPH HENRY. [1855- 

out in the wa3te-pipe would be just equal to that received 
into the boiler, provided there were no loss from conduction 
and radiation; but in the engine drawing up water, for ex- 
ample, a quantity of heat is actually annihilated in doing 
the work. The vibrations of the atoms which constitute 
heat are stopped in giving motion to the piston-rod. Con- 
versely, if the water which has been pumped up to an eleva- 
tion were made in its descent to produce heat by means of 
revolving disks, the amount generated would be just equal 
to that which disappeared in the other case. .^ . 

For practical purposes it is therefore of great importance 
that the ratio of equivalents of heat and mechanical power 
sliould be accurately determined, and for this purpose James 
P. Joule, of Manchester, has made a series of most delicate and 
beautiful experiments on the heat evolved by the revolution 
of paddle-wheels in baths of water, mercury, or oil. Motion 
was given to the paddle-wheels by a known weight descend- 
ing from a given height; the amount of heat was found to 
bo precisely the same with a given expendituio of mechan- 
ical power, whether the wheel revolved in water, mercury, 
or oil, proper allowance being made for the different densi- 
ties and the difiFerent capacities of these bodies for heat. In 
this way, he found that the fall of a weight of one pound 
through 772 feet, or what would be the equivalent, the fall 
of a weight of 772 pounds through one foot, is just suf- 
ficient to raise the temperature of one pound of water one 
degree of Fahrenheit's scale. Seven hundred and seventy- 
two pounds falling through one foot is therefore considered 
as the unit of the working power of heat; and in honor of 
the investigator who has thus enriched modern science with 
one of its most valuable means of calculation, applicable to 
every part of physical research, it is denominated "Joule's 
unit." By it we are enabled to express in terms of the des- 
cent of a weight the equivalency of all the forces of Nature, 
and thus to reduce the mechanical conception of their rela- 
tions to its greatest simplicity, and to apply mathematical 
reasoning to a variety of problems heretofore excluded from 
the province of this great logical instrument, so essential in 



•^899] WRITINGS OP JOSEPH HENRY. 137 

the deduction of effects from complex relations. The des- 
cent of a weight is chosen, because it is perhaps the most 
familiar, and of the easiest conception and application. The 
value of a fall of water is always estimated by the quantity 
of liquid multiplied by the height through which it descends. 
If we multiply these together, and divide by 772, we shall 
have the number of degrees of heat that this will impart to 
a pound of water; and conversely, by knowing the number 
of degrees of heat as measured by the number of pounds of 
water raised one degree, we shall have the number of pounds 
of water which can be elevated to a given height by a per- 
fect machine; and when such effects are submitted to this 
calculation, we find that the steam engine, in its most im- 
proved form, is far from utilizing all the heat applied to it; 
by far the greater portion is expended in the separation of 
the atoms of water in radiation, in overcoming friction, and 
in the production of vibration and useless motion. 

Mr. Joule also established the relations of equivalence 
among the energies of chemical afiBnities of heat, of combi- 
nation, or of combustion, of electrical currents in the galvanic 
battery, and in electro-magnetic machines, and of all the 
varied and interchangeable manifestations of caloric action 
and mechanical force which accompanies them. A series of 
experiments has also been made on the heat of animals, 
which is found to be the equivalent of the chemical com- 
bination of the food and the oxygen which they inhaled. 

The influence which investigations of this kind are to have 

on the future history of mechanical arts and the production 

of labor-saving machines, and on the increased power of man 

in controlling the innate forces of matter, it is impossible to 

estimate. 

" The food of animals is either vegetable, or animals fed on 
vegetables, or ultimately vegetable after several removes. 
Except mushrooms and other fungi, which can grow in the 
dark, are nourished by organic food like animals, and like 
them absorb oxygen and exhale carbonic acid, — all known 
vegetables get the greater part of their substance (certainly 
all their combustible matter) from the decomposition of 
carbonic acid and water absorbed bv them from the air and 



138 WRITINGS OP JOSEPH HENRY. [1855- 

soil. The separation of carbon and of hydrogen from oxygen 
. in these de-compositions is an energetic effect equivalent to 
the heat of re-combination of those elements by combustion 
or otherwise. The beautiful discovery of Priestley, and the 
subsequent researches of Sennebier, De Saussure, Sir Hum- 
phry Davy, and others, have made it quite certain that 
those de-compositions of water and carbonic acid only take 
place naturally in the day-time, and that light falling on the 
green leaves, either from the sun or an artificial source, is 
an essential condition without which they are never effected. 
There cannot be a doubt but that it is the dynamical energy 
of the luminiferous vibrations which is here eflBcient in forc- 
ing the particles of carbon and hydrogen away from those of 
oxygen, towards which they are attracted with such powerful 
affinities, and that luminiferous motions are reduced to rest 
to an extent exactly equivalent to the potential energy thus 
called into being. Wood fires give us neat and light which 
have been got from the sun a few years ago. Our coal fires 
and gas lamps bring out, for our present comfort, heat and 
light of a primeval sun, which have lain dormant as a 
potential energy beneath the seas and mountains for countless 
ages." (Prof. William Thomson.) 

A striking example of the transformation, as it were, of 
the force of motion into heat is exhibited by an article of 
apparatus now in the cabinet of the Smithsonian Institution 
and devised by M. Leon Foucault, of Paris. Between the 
poles of a strong elcctrio-magnct a heavy metallic disc is 
made to rotate, and although the revolving body does not 
touch the magnet, yet its motion is stopped by it in a few 
seconds. The momentum of the disc which is thus over- 
come gives rise to heat; for the redaction of the magnet pro- 
duces a current of electricity, and in the resistance to this 
tlie heat is generated. A body in motion is in a state of 
power, and it cannot come to rest without producing some 
effect on the surrounding matter. The ultimate effect in 
this case is an agitation of the atoms of the metal. 

Condition of the Earth in Space, 

Having given a general view of the atomic theory in its 
widest generalizations, we now propose to consider its appli- 
tion to the physical phenomena of our globe. For this pur- 



-1859] WRITINGS OF JOSEPH HENRY. 139 

pose we will briefly recall soiiie of the elementary facts of 
astronomy. 

The earth is a globe very slightly flattened at the poles, 
isolated in space, supported upon nothing, and only connected 
with other bodies of the universe by the all-pervading force 
of attraction. In this free space it turns upon itself with a 
regular motion around an ideal axis which pierces its surface 
at^wo opposite points or poles, which have never sensibly 
varied their position. It also moves in space describing 
around the sun in the course of a year a slightly elliptical 
curve called its orbit. But this movement of translation 
around the sun does not interfere with the rotation of the 
earth around its axis; for in accordance with the second fun- 
damental law of motion, two motions of this kind may exist 
in a body at the same time. If the earth's axis were at right 
angles to the plane of its orbit, but slight variations would 
be found in the temperature at its surface in different periods 
of the year. The axis is not however thus placed, but is in- 
clined at an angle of about twenty -three and a half degrees 
to the plane above mentioned; and this fact, which at first 
sight might appear of little consequence, in reality produces 
all the alternations- of seasons, and is connected with all the 
changes of climate of the surface of the globe. Gradual 
changes of climate cannot be produced by a change in the 
axis of rotation, as some have supposed, since this would alter 
the whole form of the earth, and produce other changes in- 
compatible with the facts of observation. 

The position, the form, and the movement of the earth are 
similar to those of the other planetary masses which we see 
isolated in space under the form of globes, turning around 
on an axis within themselves, and around the sun in ellip- 
tical curves. While we observe that the earth is the centre 
of the orbit of our moon, we sec that four moons turn around 
Jupiter, seven around Saturn, and six around Uranus. A 
planet, with the moons which accompany it, form what is 
called a planetary system^ and all the planets tixken together, 
with the sun, constitute what is denominated the solar systenu 
In this system the earth occupies the third place from the 



140 WRITINGS OP JOSEPH HENRY. [1855- 

sun, from which it is removed ninetv-five millions of miles 
at its mean distance. Neptune occupies the most distant 
limit, and is more than thirty times farther removed than 
the earth from the principal centre of influence. But these 
distances, though greatly beyond our definite conceptions, 
are nothing in comparison with the intervals which separate 
the sun from the fixed stars. These bodies like the sun are 
self-luminous, and are without doubt centres of planetary 
systems; but they are at such an inconceivable distance that 
light itself, which requires but eight minutes to reach us 
from the sun, occupies years of time in its journey from the 
nearest of them. But all the stars which are visible to the 
naked eye form only a single group, which, if viewed at a suf- 
ficient distance, would appear in the heavens as only a lumi- 
nous cloud or spot, and would resemble the nebulous patches 
which we perceive here and there in different parts of the 
heavens by the aid of powerful telescopes. This universe, 
unbounded (at least to human intelligence) — is composed of 
isolated groups of stars, and perhaps of orders of arrange- 
ment still more elevated. In this magnificent assembly our 
nebula is only a spot in the infinity of spots; our sun is only 
a star in the midst of the stars of the group to which it be- 
longs; and among the planets which revolve around our sun, 
the earth is one of an inferior order. 

Starting from the grouping of gross atoms, which we have 
previously given, and extending the analogy, the thought 
has been expressed that our earth might be compared to an 
atom ; the earth and moon to a compound atom; the whole 
system to a molecule; and our sun, and all the stars of the 
group to which it belongs, as the great solid of solids, and 
thus in one conception embracing the whole material 
univeree. But to limit our speculations we may inquire 
whether the infinity of stars by which we are surrounded 
has any influence upon the climate and temperature of 
this earth. 

Influence of the stars. — It is well known that at one time 
the stars were supposed to influence human destiny, and 
though astronomy has discarded most of the pretensions of 



-1859] WRITINGS OF JOSEPH HENRY. 141 

her progenitor — astrology, yet in this instance, modern 
science has shown that the stars have really a physical in- 
fluence upon our earth and on every other planet of our 
system. If from any point in space a line be extended in 
thought in any direction, it will ultimately meet a radiating 
body; and hence every point in space must be constantly 
traversed from all directions with radiating impulses which 
give it a definite and fixed temperature. For example, our 
sun sends a ray to every point of the universe, and every 
other sun sends a ray to the same point, and the sum of all 
these rays will constitute the temperature of that point. We 
say the temperature of that point, by which we mean the 
efifect which would be produced on a thermometer if put in 
that place; not that there is any temperature in celestial space, 
for this, as we have seen, belongs to gross matter, and is pro- 
duced by the motion of its atoms. The term however is 
convenient, and we shall continue to use it. 

If the radiating power of the suns remained without 
change, then the temperature of each point in space would 
be unchangeable. From this consideration it follows that 
the planetary space in which our earth is moving has in one 
sense a fixed temperature (independent of the heat of the 
sun,) derived from all the other suns of the universe; and 
this temperature, as we shall hereafter see, lias a marked in- 
fluence on the temperature of the globe. 

We shall return to this subject again, and at present shall 
merely state that at the polar regions of our earth during 
the months of winter, the space immediately contiguous to 
the surface is screened from the heat of the sun, and con- 
sequently the earth by its radiation, must fall in tempera- 
ture nearly to that of celestial space. A similar screening 
takes place in succession on all parts of the earth's sur- 
face during the night; and as the loss of heat by radiation 
depends (as we shall see) upon the temperature of the space 
into which the rays are sent, every part of the earth's sur- 
face must be affected more or less by the temperature of inter- 
planetary space; and if this were to vary, though our sun 
might continue constant in its emanation, the average ter- 
restrial temperature would be subject to a change. 



142 WHITINGS OF JOSEPH HENRY. [1855- 

We cannot however explain the effect of the temperature 
of planetary space upon our earth until we have further con- 
sidered the subject of heat. 

Heat of the Earth, 

The temperature of the earth is derived from three 
sources, namel)^ the original heat of the earth, the heat of 
celestial space, and the heat of the sun. Before however 
giving an account of the heat derived from these sources, 
we shall consider the character of radiant heat, as developed 
by the researches of Melloiii and others. 

Radiant Heat. — The impulses which are received from the 
sun, as we have seen, are far from being simple in their 
nature. We know that a beam from this luminary consists 
of at least four different classes of emanations, namely, of 
light, of heat, of chemical action, and of phosphorogenic 
effect. We also know that the first class, that of light, con- 
sists of a number of different emanations which produce in 
us the sensations of the different colors of the spectrum, and 
from analogy we might have inferred that the heat emana- 
tions also consist of a number of rays, possessing different 
properties, and producing at the surface of the earth differ- 
ent physical and perhaps physiological effects. 

Let us begin with heat of the lowest intensity, or that 
which is supposed to be composed of waves of the greatest 
length; for example, the radiation from a canister of hot 
water suspended in mid-air. If this have a temperature 
in the least degree above that of the surrounding bodies, 
they will increase in temperature, while the vessel itself will 
slowly cool. The rapidity of cooling will gradually dimin- 
ish in a geometrical ratio, as the temperature of the canister 
approaches that of the surrounding bodies, and they will 
finally arrive at a state of dynamic equilibrium. The can- 
ister at this point does not cease to radiate, but continues to 
send impulses in every direction, receiving as many im- 
pulses from the surrounding bodies, (including the air,) as it 
sends off from its own surface. 



-1859] WRITINGS OF JOSEPH HENRY. 143 

The heat from this source possesses peculiar properties. 
First, it is readily absorbed by all bodies^ in proportion to 
some peculiarity of the texture of their surface, but is whoUy 
independent of the color; or in other words this kind of heat, 
unlike light, is absorbed by light-colored substances as well 
as dark, and this fact would be in accordance with the hy- 
pothesis assumed, which supposes these two emanations to 
consist of waves of different lengths, and perhaps of slightly 
different form. Secondly, this kind of heat is incapable of 
passing by direct radiation through many media which arc 
freely traversed by light, such as glass, alum, and many 
other transparent substances, while it is freely transmitted 
through polished plates of rock-salt, and partially through 
many other bodies, some of which are impervious to light. 
The former class of bodies is called athermanous, the latter 
diathermanoiLS, 

Let us now suppose the radiating body to be one which 
can be increased in temperature until it becomes red-hot. At 
a certain stage of incandescence, other rays than those de- 
scribed as capable of exciting heat begin to be given oflF along 
with the former, which are distinguished by different prop- 
perties. First, they tend to be absorbed by all bodies in pro- 
portion to the darkness of their color, and approximate in 
this respect to the property of light. Secondly, they possess 
a property of transmissibility without diminution, through 
all transparent substances, through colorless media, and ii) 
various proportions through colored media, according to the 
nature of the latter. 

While bodies heated below redness give oflF exclusively 
rays of the first class, (though approaching in character those 
of the second as the temperature is increased,) incandescent 
bodies simultaneously give oflF both species. 

As the intensity of heating still further increases, rays of 
less and less length are given oflF, until they arrive at the 
limit of the perceptibility of the sense of vision, and only 
render their existence manifest by chemical and phosphoro- 
genic efiFects. 

The following table exhibits some of the results which 



( 



144 



WRITINGS OP JOSEPH HENRY. 



[1855- 



Melloni obtained by experimenting with diflFerent sources of 
beat and different substances. 



Relaiive absorbing power by different suhstanees of different kinds of heat. 



Substances. 



Lampblack . 

While lead 

Isinglass 

Indian ink 

Shellac 

Polished metal 




Incandescent 


Copper, at 


platinum. 


76op. 


100 


100 


56 


89 


54 


84 


95 


87 


47 


70 


13-5 


18 



Copper, at 
2120 Y, 



100 
100 
91 
85 
72 
18 



As an illustration of the effects of radiant heat of different 
kinds, we may mention the fact, long observed, of the melt- 
ing of snow near the trunks of trees and other dark-colored 
bodies. That this effect is not due to the natural heat of the 
plant is evident from the fact that it is equally exhibited 
around the stumps of dead trees, and dark-colored objects of 
an entirely different character. The rays of heat from the sun, 
(as before stated,) possessing similar properties to those of 
light, are absorbed by dark substances, and freely reflected 
from light ones. The facets of the small crystals of snow re- 
flect this heat almost entirely, while it is absorbed by the 
(lark surface of the wood of which it raises the temperature, 
thus producing a new source of emanation. The heat how- 
ever given off from the wood, is that of long waves of low 
intensity, which is equally absorbed by light and dark 
bodies; hence it enters the snow, raises its temperature, and 
converts it from a solid to a liquid condition. We may im- 
itate this action • by supporting at a little distance above a 
surface of new fallen snow a piece of pasteboard, both sides 
of which have been covered with lampblack, and the whole 
freely exposed to the sun*s rays. It will be found that the 
melting of the surface within the shadow is much more 
rapid than that exposed to the direct rays of the sun. The 
same result may be produced by the rays from an argand 
lamp. Having IBHed a square box with new fallen snow 



-1859] WKITINQS OF JOSEPH HENKY. 145 

slightly packed, and all above the rim having been removed 
by means of a ruler, so as to present a uniformly plain sur- 
face, the box is turned on its side opposite the lamp, and the 
pasteboard interposed. In a short time the plain surface of 
snow will be hollowed out beneath the disk, and at the end 
of half an hour the cavity will be several lines deep at its 
centre. When the same experiment is repeated by substi- 
tuting for the lamp an iron ball heated to about 400° F., the 
phenomena present themselves in a reverse order, that is to 
say, the melting of the snow would be more abundant where 
the direct rays impinge on the surface, than where they are 
intercepted by the interposed disk, and instead of a hollow, 
a protuberance would be produced at the centre of the shaded 
portion. If we substitute in this experiment for the black 
disk of pasteboard one covered with white lead, the heat will 
not be absorbed, but will be reflected as from the snow itself. 

Another example of the transmission and, as it were, 
transformation of radiant heat from the sun is afforded in 
the high temperature produced by the ordinary hot-bed of 
a garden. The solar rays, consisting of short vibrations, 
readily pass through the glass cover, and are absorbed by 
the dark ground, the atoms of which they put into more 
rapid vibration, and these in turn give rise to new emana- 
. tions, which consisting of long waves are arrested by the glass, 
and the terpperature of the enclosed space is thus constantly 
increased. It is also on the same principle that the radiant 
heat of a stove does not pass out into space through the win- 
dows of a house, though a considerable portion of the radi- 
ant heat from an open fire would be lost in this way. 

We may apply the foregoing principles to explain the 
accumulation of heat at the surface of the earth. The trans- 
parent envelope which covers the surface of our planet is not 
entirely diathermanous; and though it transmits freely the 
intense rays of the sun it stops those of the long vibrations. 
The surface of the earth is then in the condition of the ground 
under the glass of the hot-bed; it is constantly absorbing 
and receiving heat of high intensity, and constantly radi- 
ating heat of intermediate intensity. Let us suppose all 

10-2 



146 WRITINGS OF JOSEPH HENRY. [1855- 

heat removed from the earth, and the sun suddenly allowed 
to shine upon it. In this ease, all the rays which travereed 
the atmosphere and reached the earth would be absorbed. 
None would be radiated into space until the temperature of 
the surface was so elevated that the rays emitted from it 
could permeate the atmosphere. 

The surface of the earth at first would therefore receive 
more rays than it gave off. Its temperature would increase 
and with each increase of temperature a greater number of 
rays would be produced of such intensity as would enable 
them to permeate the atmospheric envelope, and finally an 
equilibrium would be attained in which the rays sent oflf in a 
given time would be just equal in number to those receiyed. 

The point of temperature at which this equilibrium would 
take place will depend on the height and permeability of the 
atmosphere. If the aerial envelope offered no impediment 
to the escape of heat of the lowest intensity, the equilibrium 
would take place at so low a temperature that all bodies 
capable of freezing would be perpetually in a solid state. If 
on the other hand the atmosphere were more dense than it 
is, or in other words, more impervious to rays of a higher 
intensity than those which now pass through it, the tem- 
perature of the surface of the earth would increase until the 
heat given oflf would again be equal to that received. The 
new equilibrium would be permanently retained, and the 
whole average temperature of the surface of the globe would 
be elevated. 

Heaifrom the Stars. — The temperature therefore of the sur- 
face of a planet depends upon the nature of its atmosphere, 
provided the heat which falls upon it is derived from a 
source of high temperature : now radiations from the stars 
are of this character, since they come from self-luminous 
bodies, which are probably suns of other systems. The 
radiations from them can therefore readily pass through 
our atmosphere, and excite heat vibrations in the surface 
materials of the earth. The intensity of these vibrations 
must increase until it becomes so great that the radiations 
produced can permeate the aerial covering, and in this way 



-1859] WRITINGS OP JOSEPH HENRY. 147 

even the beat of the stars may so accumulate as sensibly 
to contribute to the temperature of the earth. Though at ' 
first sight it may appear that the effect from this source must 
be exceedingly feeble, yet when we reflect that the heat of 
the stars comes from every part of the whole concave 
of the heavens, while that of the sun proceeds from a disk 
which occupies only the five-millionth part of the whole sky, 
we may be inclined to attribute to the stellar radiation a 
much greater importance than without this reflection we 
should ascribe to it. 

M. Pouillet, of Paris, has made a series of very ingenious 
researches on the subject of the temperature of space, and 
has arrived at very unexpected results. He employed in 
his observations an instrument to which he gave the name 
of " actinometer," or ray-measurer. It consisted of a cylin- 
drical box of polished silver, about eight inches in diameter, 
and five in height, enveloped in swan's-down, and enclosed 
in an outer cylinder, so as to prevent as much as possible the 
effect of the temperature of the circumambient air. The 
box was filled with several layers of swan's-down, so sup- 
ported as not to press upon each other. In the centre of 
the upper surface of the open box was placed the bulb of a 
thermometer, the stem projecting horizontally. A cylindri- 
cal border was raised round the edge of the box, to cut off 
tlie lateral rays, and at such a height that two-thirds of the 
whole sky could be seen by an eye at the point occupied by 
the bulb. The thermometer thus enclosed was turned dur- 
ing the night to the zenith, and exposed to the radiation 
from the clear sky. The temperature of this thermometer 
and one exposed to the air at four feet from the ground was 
observed hourly. 

If the heat of the surrounding air were entirely excluded 
from the enclosed thermometer, it is evident that it would 
only be affected by the radiation from celestial space, and 
from the atoms of the air in the column between it and tlie 
top of the atmosphere. 

Of these two sources of radiation one, namely that of celes- 
tial space, would be constant and remain the same during 



148 WRITINGS OF JOSEPH HENRT. {1855- 

the whole night, as well as diflFerent nights, while the other, 
namely the radiation from the air, would vary from hour to 
hour, since it depends on the varying temperature of the at- 
mosphere. 

By obtaining a series of observations in different states of 
the atmosphere an assumption could be made as to the fixed 
temperature of space which, when subtracted from the temp- 
erature observed, would give the radiation of the column of 
the atmosphere. 

Since it was impossible to cut off all the heat from the in- 
strument except that which it received from the sky and air 
above, and since it was exposed to but two-thirds of the 
celestial hemisphere, some correction was necessary to reduce 
the observed temperature to the true one. This was found 
by making an artificial sky, formed of a zinc vessel about 
forty inches in diameter, the bottom coated with lampblack, 
and the whole filled with a refrigerating mixture. Beneath 
this the " actinometer " was vertically placed at such distances 
as to expose it successively to one-quarter, one-third, and two- 
thirds of the hemisphere; and by repeating these experi- 
ments with different temperatures of the artificial sky, it was 
found that if from the temperature of the surrounding air f 
of the lowering temperature of the actinometer were taken 
away, the temperature of the artificial sky would be obtained, 
since the same ratio would obtain in the case of the real sky. 
In order to find therefore in all future experiments the temp- 
erature which the actinometer ought to assume under the 
radiation from space and the air above, it was only necessary 
to subtract the degree given by the instrument from the 
temperature of the surrounding air and multiply this by 
■|. From a series of observations thus corrected, he found 
for the fixed part of the temperature given by the instru- 
ment, or in other words the temperature of space, a value of 
— 142° Cor — 222° F. This temperature is much lower than 
that obtained before from considerations of a more theoret- 
ical character. M. Pouillet however thinks ttiat it cannot 
be far from the true temperature of celestial space, since a 
thermometer placed upon the coldest part of the earth and 



-1859] WRITIKOS OF JOSEPH HENRY. 149 

exposed to the clear sky, always falls by its own radiation 
several degrees lower than the temperature of the air; which 
it would not do if the temperature of space were not lower 
than — 60°, since as it approached that temperature at places 
near the pole, the extra cooling from exposure to the sky 
would be very little. Mr. Espy concludes, from theoretical 
data, that the estimate of Pouillet is near the truth. 

Pouillet finds, from the data given above, that the total 
quantity of heat which space transmits in the course of a year 
to the earth and atmosphere, would be sufficient to melt a 
stratum of ice upon our globe of 85*28 feet in thickness. 
From other investigations of a similar character, which we 
shall presently describe, he finds that the quantity of solar 
heat received by the earth in the course of a year is sufficient 
to melt 101*68 feet of ice. From these two sources together 
then the earth receives a quantity of heat sufficient to melt 
187 feet of ice. These results are of so unexpected an amount 
that though obtained by instruments and methods which 
are apparently unexceptionable, they have not fully obtained 
acceptance, and the subject is therefore still open for further 
examination. 

Terrestrial temperature. — If the earth were exposed in space 
without an envelope and without receiving radiation from 
any source, it would sink to the zero of temperature, or that 
at which the atoms would cease to vibrate, and this, accord- 
ing to the mechanical theory of heat, would be about 500° 
below the freezing point of Fahrenheit's scale. 

If the earth were exposed without an envelope to the tem- 
perature of space it would, according to the results obtained 
by Pouillet, fall to — 222° of the same scale. 

With the present envelope and stellar radiation it would 
stand at — 128°. The heat necessary to make up the actual 
temperature of the earth beyond this degree is due to the 
sun's accumulated heat under the envelope. 

Eouillet has also made a series of researches on the abso- 
lute amount of heat from the sun. He used in his inves- 
tigations an instrument to which ho gave the name of 
pyr-heliometer (measurer of the heat of the sun). It con- 



150 WRITINGS OP JOSEPH HENRY. [1855- 

Bisted of a flat cylindrical vessel, the top of which was of thin 
silver, of about four inches in diameter and six-tenths of an 
inch in height or thickness. It was filled with 100 grammes 
of distilled water, and in the middle of this liquid was placed 
the bulb of a thermometer with a fine bore and a long stem 
projecting downward in the direction of the axis of the 
cylinder through its lower surface. 

The observations were made in the following manner: 
The upper surface of the vessel, coated with lampblack to 
render it absorbent of heat, was turned directly towards the 
sun, the water being kept in a state of constant agitation in 
order to equalize the heat. The increase of temperature re- 
ceived from minute to minute in the course of five minutes 
was noted. The vessel was then placed in the shade while 
its face was exposed to a portion of clear sky near the sun, 
and the loss of temperature from minute to minute during 
five minutes was*again noted. A little reflection on the 
principles of the interchange of heat, according to which 
bodies are constantly radiating even while they are receiving 
heat from other bodies, will render it evident that in order 
to find the amount of temperature communicated by the sun 
in a minute of time we must add the loss of temperature 
during the shading of the instrument to the gain of tem- 
perature notfcd during the direct exposure to the sun, for 
while the instrument was receiving heat from the sun it was 
at the same moment radiating heat to that body. To find 
from the indications thus obtained the absolute amount of 
heat which falls on the face of the vessel in one minute of 
time we must make a correction for the absorption of heat 
by the metal, and allow for the specific heat of the water, that 
is, the relative quantity necessary to elevate a pound of this 
liquid one degree of Fahrenheit's scale. In this way the 
quantity of heat which falls on a given surface, (say a square 
foot,) perpendicular to the solar beam at the surface of the 
earth is determined. But this quantity is not all that would 
be given to the same surface were the atmosphere removed, 
or if the same experiment were made at the outer limits of 
the aerial covering of the globe. A portion of the heat is 



-1859] WRITINGS OP JOSEPH HENRY. 151 

absorbed and another portion reflected from the atoms in its 
passage through the air, and in the solution of the problem 
under consideration it became necessary to know the amount 
of loss from this cause. To ascertain this the experiment 
was made while the sun was on the meridian and at diflferent 
degrees of elevation even down to near the horizon. The 
diameter of the earth, the approximate height of the atmos- 
pherO) or the length of the column of air traversed by the 
ray which passes from the zenith, and also the angle of 
elevation of the sun being given, the lengths of the several 
lines through the atmosphere traversed by the respective 
rays were readily calculated; and if we suppose that the 
amount of heat received at the outer limit of the atmosphere 
is invariable it is not difficult to determine the part which 
is absorbed. The numbers obtained by observation con- 
sisted of two quantities, a constant and a variable one; the 
former being the heat of the sun, and the latter the amount 
absorbed in passing through the different lengths of atmos- 
phere. 

From these data the amount of heat received from the sun 
on a square centimetre at the limit of the atmosphere, (and 
which it would equally receive at the surface of the earth if 
the air did not absorb or reflect any of the incident rays,) was 
ascertained to be 1*7633 units of heat in one minute of time: 
equivalent to 11*376 units per square inch, in the same period. 
It was also found that the atmospheric absorption of the rays 
directly from the zenith was comprised between eighteen 
and twenty-five-hundredths of the whole, even incases where 
the sky was perfectly clear. 

The quantity of heat which the sun sends to one centi- 
metre of the earth's surface during one minute of time by 
its perpendicular action having been determined, it was not 
difficult to ascertain the total quantity of heat received by the 
whole illuminated hemisphere in the same time. Indeed this 
quantity is nearly the same as that which would fall on 
the plane of a great circle of the earth. From this can 
be readily deduced the amount of heat which would be dis- 
tributed over the entire surface of the earth during a year; 



152 WHITINGS OF JOSEPH HBNBY. [1859- 

and this was determined to be 231,675 units falling on each 
square centimetre of the whole surface. Calculating the 
amount of ice which this quantity of heat would melt* 
Pouillet obtained a thickness of 30*89 metres, or a little more 
than 101 feet; that is, if the total quantity of heat which the 
earth receives from the sun in the course of a year were uni- 
formly distributed over all points of the globe, and were 
employed without' loss in dissolving ice, it would melt a 
stratum having the above thickness. 

The data given by these experiments enabled him to 
solve another problem which would appear even of a more 
transcendental character : that is, the amount of heat given 
off by the whole surface of the sun in a given time. For this 
purpose it is only necessary to consider the sun as the centre 
of a spherical enclosure, the radius of which is the distance 
from the earth to the sun ; * and it must be evident that on 
each square centimetre of the concave surface of this vast 
sphere as much heat is received as on a square centimetre 
at the surface of the earth. If then the number 1*7633, 
before obtained, is multiplied by the number of square centi- 
metres in this spherical surface the absolute quantity of 
heat given off by the sun during a given time will be ascer- 
tained. Or by reference to the visual angle subtended by 
the sun, the number expressing this quantity for each minute 
of time may be stated as 84,888 thermal units for each square 
centimetre of the solar surface. 

If this quantity of heat emitted by the sun were exclusively 
employed in dissolving a stratum of ice, applied to the solar 
surface, and enveloping it on every side, it would melt in 
one minute a stratum of 11*8 metres thick ; and in one day 
a stratum of 16,992 metres, or about lOJ miles. 

These results cannot be considered more than approxi- 
mations, though in the progress of science, they may bo 
rendered much more precise, and may be applied to solve 
many problems relative to the physical phenomena of the 
earth and our solar system. 

♦The proportional amount of the entire solar nidiation intorcoptwl by tbo 
terrestrial hemisphere is 1 -^ 2 300,000000. 



-1859] WRITINGS OP JOSEPH HENRY. 153 

Original heat of Uie earth. — Besides the smaller influence of 
celestial space, and the governing one of the emanations from 
the sun, there is another source of terrestrial heat, which, 
though it at present produces scarcely an appreciable effect 
upon the temperature of the surface, was once powerfully active 
in effecting geological changes, and in so modifying the sur- 
face of our planet as to give rise to the diversities of surface 
constituting mountains, seas, and continents, which now 
determine the varieties and peculiarities of our present cli- 
mates, and may in the future be of vast practical value in 
its applicability to the wants of life. We allude to the in- 
ternal heat of the earth. 

That the earth was once at least in a liquid condition by 
heat, can scarcely be doubted, when all the cumulative evi- 
dence in favor of the hypothesis is considered. 

First Self-luminous bodies are met with in every part of 
the visible universe, and if we follow the strict inductive pro- 
cess, allowing no more causes than are true and suflicient, 
we must admit that these bodies are intensely heated. It is 
therefore not impossible that the earth itself may have been 
at one time a self-luminous star. 

Second. The surface of our moon, though it now gives lit- 
tle or no indication of heat, appears when viewed through a 
powerful telescope almost covered with the craters of extinct 
volcanoes ; and hence we may infer that it has cooled down 
from a high temperature to its present condition. 

Third. Every portion of the earth's crust exhibits the re- 
mains of igneous action, and the facts of geology are inex- 
plicable on any other hypothesis than that of the past high 
temperature of our globe. 

Fourth. On every part of the earth where the experiment 
has been made, starting from the point where the sun's 
influence ceases, there has been found an increase of tem- 
perature as we descend toward the centre, at the rate of about 
a degree for every fifty feet. 

Fifth. On different parts of the earth's surface springs 01 
hot water are found bursting forth. 

Sixth. There are on the surface of the earth several hun- 



154 WRITINGS OP JOSEPH HENRY. [1855- 

dred volcanoes, which occasionally emit heated materials, 
and in some cases incandescent lava. 

Seventh. The oblate form of the earth is on an average 
that which would be due to the rotation of a liquid mass. 

From all these facts we may now safely admit as a definite 
theory, the hypothesis which was at first a mere antecedent 
probability, namely, that the earth was at one time in a 
highly heated state, and that its interior, even at the present 
moment, is still at a very elevated temperature. If we apply 
this hypothesis to the facts of geology as they are generalized 
and arranged at the present daj% we have a complete ex- 
planation of the whole; or if there be any outstanding 
phenomena not yet included in this generalization, their 
number is so small in comparison to those included in it, 
that they may reasonably be left for the present until further 
discovery shall throw more light upon their character. The 
great principle of universal gravitation was not abandoned 
though at one time several facts in regard to the motion of 
the moon could not be referred to it. The same considera- 
tion applies to moral subjects as well as to those of science. 

Equilibrium of the Atmosphere. 

The aerial covering which surrounds our earth may be 
compared to an ocean, of which the bottom is composed of 
land and water, which has a definite surface above, probably 
agitated by tidal waves of great extent and magnitude. 
Although nearly eight hundred times lighter than water at 
the surface of the earth, yet it possesses a very appreciable 
weight, since a cubic yard of it weighs about two pounds, 
and consequently when moving with high velocities it pro- 
duces great mechanical effects upon bodies subjected to its 
momentum. 

This ocean, unlike the aqueous ones belonging to our earth, 
diminishes in density very rapidly as we ascend, and finds 
its limit at that elevation at which the repulsion of the last 
layer of atoms added to the centrifugal force of the earth's 
rotation is just balanced by the attraction of gravitation. 



-1859] WRITINGS OP JOSEPH HENRY. 155 

In order to simplify the conditions and to give precise ideas 
of the mechanical equilibrium of the atmosphere we will at 
first suppose it to be a body consisting of simple atoms, 
which though they obey the attraction of the earth repel 
each other. This repulsion increases, as we have said in our 
exposition of the atomic theory, with a diminution of the 
distance of the atoms — a fact which may, perhaps, be best 
illustrated by a portion of air confined by a movable pis- 
ton in a tube closed at the bottom, as in the case of the ordi- 
nary fire syringe, the well known instrument used for igniting 
tinder by means of the condensation of a portion of air. If 
such an instrument be placed under the receiver of an air- 
pump, and the pressure of the atmosphere be removed from 
it, the air which is contained under the piston will expand; 
and if the tube be sufficiently large this expansion will con- 
tinue until the repulsive energy of the atoms under the pis- 
ton is just equal to the weight of the piston itself. If we 
now double the weight of the piston it will descend until 
the air is compre3sed into half its first volume. At this 
point a new equilibrium will take place between the weight 
of the piston and the repulsive energy of the atoms. If 
another addition be made to the weight of the piston it will 
descend through another distance, and in all cases the com- 
pression will be iiri»ersely proportioned to the weight applied ; 
but the density of the air, that is, the weight for a given 
quantity increases as the bulk diminishes, and therefore in 
all cases of a gas the density or the number of ponderable 
atoms in a given space will be inversely proportioned to tlie 
pressure applied. 

This fact was discovered independently by an English and 
a French philosopher, and is generally known by the name 
of the discoverers, namely, the law of Boyle and Mariotte, 
but perhaps more frequently it bears the name of the latter. 

The same law applies to all other gases within certain 
ranges. In the case of atmospheric air, within the limit of 
experiment it appears to hold without variation, or if any, 
with a very minute one, when great pressure is applied in 
connection with a great reduction of temperature. In tlie 



156 WRITINGS OF JOSEPH HENRY. [1855- 

case of carbonic acid, the range of distance of atoms is much 
less in which this law is found ; for by mechanical pressure 
the gas is converted into a liquid, a sudden change taking 
place in the intensity of the repulsion of the atoms at this 
point. Vapor of water, separated from the liquid which 
produced it, obeys the same law as that of air ; but in this 
instance the range of atoms is still more limited than in that 
of carbonic acid, and with a slight pressure, and at the ordi- 
nary temperature of the atmosphere, the vapor is converted 
into a liquid. 

The atmosphere being subject to the law of Mariotte, we 
shall now proceed to inquire what will be its condition of 
equilibrium or rest. 

First. If we suppose the whole atmosphere surrounding 
the earth to be divided into a series of strata of equal weight, 
as thin as may be necessary, and separated by ideal surfaces 
perpendicular to the plumb line, these surfaces will rest 
upon each other, and be in a state of equilibrium when each 
part of the same stratum is of the same density. 

Second. In order to a stable equilibrium, the density of 
each stratum must diminish from below upward. 

Third. The upper stratum must be below the point where 
the centrifugal force, derived from the rotation of the earth, 
becomes equal to the weight of the air at this point. 

If the first condition is not fulfilled, (that is if the equality 
of the density of the strata be not the same at all points,) the 
heavier parts will flow below those which are less dense, and 
buoy them up in the same manner as the heavier liquid sinks 
below the lighter one; and it is evident that if the upper 
strata were heavier than the lower ones, an unstable equi- 
librium would be produced which the slightest agitation 
would overthrow. 

Lastly, if the atmosphere extended upward above the 
point where the centrifugal force equalled the weight of the 
gas, the whole atmosphere, strange as it may appear, would 
fly oflF into void space. To explain this, it is necessary to 
demonstrate the important though paradoxical fact which 
results as a logical consequence of the law of Mariotte, 



-1859] WRITINGS OP JOSEPH HENRY. 157 

that the total height of an atmosphere surrounding a planet 
does not depend upon the quantity of gas of which it is 
constituted. To prove this, let us imagine a vertical column, 
say an inch square at the base, filled with air of a given 
density extending to the top of the atmosphere. Let us 
suppose this column to be divided into portions an inch 
high throughout its whole length by movable planes, and 
into each one of these portions double the quantity of air to 
be introduced. The lowest portion, namely, the first inch, 
will not be enlarged by this condition; for though twice as 
many repellant atoms are introduced into the same space, 
tending to repel upward the first dividing plane, yet this 
plane will be pressed downward by twice the weight, because 
twice the number of atoms have been introduced into all 
the strata above. 

The same reasoning may be applied to all the successive 
strata untilwe come to the very highest. On this no addi- 
tional weight is placed, and it would therefore expand until 
the diminution of its elasticity just equals its own weight, 
and at this point the equilibrium will take place. If how- 
ever this point should be just at the place of equilibrium 
where the weight of the atom would be overcome by the cen- 
trifugal force, the upper film would be removed, another 
would expand into its place, and another, and another, until 
the whole atmosphere would be withdrawn. This, as we 
have said, is a logical consequence of the extension of the 
law of Mariotte, and has been applied by Dal ton and others 
to determine the heights of mixed atmospheres, or of atmos- 
pheres of different densities. But the height of the atmos- 
phere, is probably far below the point where the weight of 
the atom is equal to the force of gravity, since this may be 
found by calculation to be at about 5*6 times the earth's 
radius from the surface at the equator, or about 22,400 miles. 
If we suppose the column to be formed of a lighter gas, as 
for example hydrogen, the atoms of which have the same 
repulsive energy as those of air, then the column will be in- 
versely proportioned to the density at the surface, and from 
this we can readily calculate the relative heights of atmos- 



158 WRITINGS OF JOSEPH HENRY. [1855- 

pheres of diflferent gases, having different densities at tlie 
surface of the earth. These heights will evidently be in- 
versely as the densities, or in other words the specific grav- 
ities, of the same gases under the same pressure. If the 
specific gravity of hydrogen be represented by 1, that of 
nitrogen in round numbers will be 15, that of oxygen 16, 
and that of carbonic acid 22, and the total heights of atmos- 
pheres of these gases will be inversely as these numbers; or 
if we call the height of an atmosphere of oxygen 60, then 
the heights of atmosphere of these gases will be as follows : 



GkiBes. 


Specific gravity. 


Height of 
atmospheres. 


Hydrogen 

Nitrogen , 

Oxygen 

Carbonic ftcid ..._._. « ...«. 


1 
15 
16 
22 


960 
64 
60 
44 







In the foregoing the repulsive energy has been considered 
as increasing in conformity with the law of Mariotte, directly 
as the pressure and without regard to the increase of repul- 
sion caused by heat; but if we suppose that the -repul- 
sion of the atoms of the lower stratum is increased by heat, 
they will be farther separated, and the space occupied by 
them enlarged. But if ^lie heat extends upward through 
the whole, each of its parts will be uniformly expanded, 
and hence the relative height of atmospheres of different 
grades will not be altered by an increase of heat, provided 
this increase is the same in each gas. The absolute heights 
will however be increased ^J-g^ part for each degree of Fahren- 
heit's scale above its volume at the freezing point. 

In order to obtain or determine an equilibrium of the at- 
mosphere when the natural repulsion of the atoms is in- 
creased by heat, each stratum as we ascend must at least con- 
tain the same amount of caloric. In this case, if a quantity 
of air be removed from a 1ow(t to a higher position, it will 
expand on account of the reduced pressure, and the same 
amount of heat being now difiused through a larger space, 
the intensity of its action or its temi)erature will fall, and 



-1859] WRITINGS OP JOSEPH HENRY. 159 

thus a reduction of sensible heat will be observed as we as- 
cend in the atmosphere. The equilibrium we have described 
would not however be a stable one, and hence the upper 
strata of the atmosphere contain more heat per pound than 
the lower. 

Until about the middle of the last century, the atmosphere 
was supposed to consist of one simple homogeneous substance, 
and after modern chemistry had discovered it to be a com- 
pound, the ingredients were thought to be chemically united.. 
It was also supposed, until the researches of Dalton proved 
the contrary, that the vapor of water found in the atmos- 
phere was dissolved in it, as one liquid is dissolved in 
another. 

Dalton was the first to advance the proposition tliat the 
atoms of different gases neither attract nor repel each other ; 
and though each offers a slight mechanical obstruction to 
the free motion of the other, yet if suflBcient time be allowed, 
each will arrange itSelf as if the other did not exist ; or in 
other words while the atoms of the same gas repel one 
another, those of different gases exert no action of this kind, 
and are in fact statical though not dynamical vacuums each 
to the other. The fundamental fact on whicli this theory 
is based is the following: If two wide-mouthed jars be 
placed, one on the other, mouth to mouth, the lower one 
being filled with oxygen or heavy gas, and the upper one 
with hydrogen, the lightest of all gases, and thus suffered 
to remain, after a short time it will be found that the two 
gases will be thoroughly mingled through both jars; the 
light gas will descend and mix with the heavier, while the 
heavier will in turn ascend and mix with the lighter. 
There will be no increase or diminution of bulk of the two 
gases after they have thus mingled. In order to explain 
the mixing of gases, three hypotheses may be assumed : 

First. We may suppose that the atoms have an affinity 
for each other in their gaseous state. But if this were the. 
case, from general analogy there should be a diminution of 
the bulk ; the number of centres of repulsion would be 
diminished, and also the. intensity of the action of each 
would be at least partly neutralized. 



160 WRITINGS OF JOSEPH HENRY. [1855- 

Secondly. We may suppose that the two classes of atoms 
repel each other, but in this case no mixture could take place; 
the heavier gas would remain in the lower vessel, while the 
lighter one would occupy the upper position. 

Thirdly. If we suppose the atoms of the two gases have 
no action on each other, but are free to obey their own re- 
pulsions, then the atoms of each gas will expand into the 
void space of the interstices of the other, and the diffusion 
indicated by the experiment will be produced. 

It follows from this hypothesis that th^tiCiilk 5f thd^ihix- 
ture should remain the same before and after the mingling 
' takes place. Let us suppose each vessel to contain a foot of 
gas, and that the repulsive energy is suflScient to sustain a 
weight of 15 pounds to the square inch; and let us suppose 
the interior of the vessel containing the hydrogen is a vacuum. 
Then it is evident that the oxygen in the lower vessel, being 
relieved from the pressure of the atmosphere, will expand 
and fill both vessels, and by the law of Mariotte, its elastic 
force or repulsive energy will be reduced to one-half or-7J 
pounds to the square inch. The same will take place with 
regard to the hydrogen. It will expand downward and fill 
both vessels, and its elastic force will be reduced to one-half 
or to 7J pounds to the square inch. If therefore the gases 
are vacuums to each other, they will each expand into the 
other and form a mixture of two gases, the pressure of each 
of which against the sides of the vessel will be 7J pounds 
to the square inch, and consequently the whole pressure will 
be 15 pounds. 

The theory of Dalton is in exact accordance with all the 
facts, though it may be difficult to conceive of atoms, such 
as those of oxygen and hydrogen, as being without action 
on each other particularly when highly compressed. In- 
deed, Mr. Dalton in the latter part of his life was inclined 
to refer this seeming want of repulsion to the fact of the dif- 
ferent sizes of the atoms, or in other words to the difference in 
the spheres of their repulsive energies. If two classes of 
atoms were thus mingled with each other, it is evident that 
they could not be in equilibrium until the one was generally 



-1859] WRITINGS OF JOSEPH HENRY. JgJ 

diffused through the other; this would give a ready explan- 
ation of the diffusion of the two gases through each other in 
close vessels. But it does not seem to us to be applicable to 
the explanation of free atmospheres co-existing on the sur- 
face of the earth, as appears to be the case, particularly with 
reference to the gases and aqueous vapor of the atmosphere. 
I have dwelt upon this point because very erroneous ideas 
are frequently entertained as to the theory of Dalton, which, 
whatever may be its truth, has had a very important bear- 
ing on the progress of meteorology. By one class of writers 
on the subject it has been the basis of all investigation, and 
by anotlier it has been too much neglected. All our hygro- 
metrical calculations relative to the amount of water in the 
air rest upon it. While there remains but little doubt that 
if the air, as a whole, were at rest, and sufficient time were 
given for the establishment of an equilibrium, the several 
ingredients would arrange themselves in accordance with 
this theory; yet, since the atmosphere is constantly agitated 
with currents, and diffusion is carried on more rapidly 
through this agency than- that from the self-repulsion of the 
atoms, we can only suppose that there is merely a constant 
tendency (particularly in the lower strata of the atmosphere) 
to assume the statical condition indicated by the theory. 

Ckympositioii of the Atmosphere. — At the level of the sea and 
at all accessible heights our atmosphere principally consists 
of a nearly invariable mixture of two permanent gases, 
oxygen and nitrogen, and a number of variable substances, 
of which we enumerate carbonic acid, nitric acid, am- 
monia, hydrogen, mineral powders, animal and vegetable 
matter, odoriferous substances, and above all a considerable 
quantity of water in a state of invisible vapor, and that of 
partial condensation in the form of cloud. Indeed, it must 
be a reservoir of all the emanations which arise from the 
decomposition of animal and vegetable matter, and which 
are given off from all substances in minute quantities under 
the application of heat. Though the variable portions of 
the atmosphere form but a small percentage of the whole 
mass, yet they exert an important influence on animal and 
U-2 



162 WRITINGS OF JOSEPH HENRY. [185S- 

-vegetable life, and deserve the special attention of the agri- 
cultural chemist. 

Analysis of the Air. — But before proceeding to give an 
account of these, it may be well to pause here for a moment 
to describe the simplest method by which the constitution 
of the air may be approximately analyzed. For this pur- 
pose we introduce into a large glass vessel filled with ordi- 
nary air a small quantity of limpid lime water, or better 
still, baryta water, and having closed the vessel agitate the 
liquid. All the soluble substances, including the carbonic 
acid, will be absorbed. The latter will unite with the lime 
or baryta water and form insoluble carbonates, which may 
afterwards be separated from the water, dried and weighed, 
and the amount of carbonic acid thus determined. To obtain 
the amount of vapor in a given quantity of air the latter is 
drawn through a tube containing chloride of lime, a sub- 
stance which has a great affinity for moisture. The increase 
of weight found after the process will indicate the amount 
of water in the portion of air submitted to the experiment. 
The volume of this air may be readily ascertained by attach- 
ing the tube containing the chloride of lime to the upper 
part of a vessel, say a cubic foot in capacity, filled with water, 
from which the liquid is suffered to run out by an orifice 
at the bottom; an equal bulk of air will enter through the 
tube containing the chloride, and when all the water has 
run out, the vessel will bo filled with air, or in other words, 
one cubic foot of the moist atmosphere will have passed 
through the drying tube. The quantity of aqueous vapor 
is more variable than that of the carbonic acid. 

After having separated the water and carbonic acid, in 
order to ascertain the amount of oxygen and nitrogen in a 
cubic foot of air, we burn in the mixture a piece of phos- 
phorous, which combines with every atom of the oxygen, 
forming a soluble substance called phosphoric acid, which is 
absorbed by the water, leaving the nitrogen in a separate 
state. Other and more refined methods are frequently em- 
ployed, but this will serve to indicate in a general way the 
mode in which the results are obtained. In this manner, 



-1859] WRITINGS OF JOSEPH HENRY. 163 

we find that the atmosphere consists of 2001 parts of oxygen 
to 75*29 of nitrogen in volume, or 2301 parts, by weight, of 
oxygen and 7639 of nitrogen. These numbers are not pre- 
cisely those which would result from a chemical union, as 
was at first supposed, namely, one volume of oxygen and 
four of nitrogen. They are not also entirely invariable, but 
are found to diflfer slightly at diflTerent places at the level of 
the sea. Observation has not shown any appreciable varia- 
tion from year to year, though it is not improbable that dur- 
ing the geological periods changes have taken place in its 
proportions as well as in its amount. The quantity of car- 
bonic acid is found, by the mode we have described, to vary 

from the xiAnr ^ nAnr ^^ ^^® weight of the whole. 

Oxygen, as we have seen in the exposition of the atomic 
theory, is a very energetic element widely diffused through 
nature, and performs an important part in the transforma- 
tions of inert matter into plants and animals, and back again 
into carbonic and other inorganic compounds. The nitro- 
gen also is an important element in vital economy, and is 
associated with all the most instable organic compounds. 
Its atoms appear to exert a great repulsive energy on each 
other; and hence, when confined in a solid state by sur- 
rounding atoms of other substances, the slightest jar will 
overturn the instable equilibrium, and produce a violent ex- 
plosion. 

Carbonic acid is a transparent substanccf that is produced 
when charcoal is burnt in air or oxygen, and is composed 
of one atom of the former to two of the latter, or three parts 
of one to eight of the other by weight. It furnishes the car- 
bon of the plant, and though it exists in small quantities in 
the atmosphere, animal and vegetable life could not be con- 
tinued on the surface of the globe without it. The quantity 
of carbonic acid contained in the air varies between the 
hours of night and day, the quantity being at its maximum 
towards morning, and its minimum towards the middle of 
the day. In this respect it follows a law analogous to that 
of the heat and moisture of the atmosphere. A part of this 
variation may be referred to the absorption of carbonic acid 



164 WRITINGS OF JOSEPH HENRY. [1855- 

by plants during the day, though this cannot be the prin- 
cipal cause; a more efficient one is probably the varying 
quantity of moisture, which may serve as a kind of vehicle 
for its transportation to and from the ground. There is 
also a great difference in the amount of carbonic acid in dif- 
ferent places, perhaps in different countries, and it is pos- 
sible that a part of the variations of fertility, the other con- 
ditions being the same, may in some cases be referred to this 
cause. We find, from experiment, that vegetation is favored 
by the increase of this ingredient until, according to Saus- 
sure, we arrive at the proportion of eight parts to one hun- 
dred, which is eighty times more than the ordinary quan- 
tity existing in the atmosphere. Tlie same portion would 
entirely extinguish the life of the red-blooded air-breathing 
animals. It is on this fact that some geologists have founded 
the hypothesis that the luxuriant vegetation which existed 
on the earth during the coal period was due to an atmos- 
phere charged with carbonic acid, and the ampliibious char- 
acter of the animals existing at that period would seem to 
favor this supposition. 

M. Chevandier has shown that one square mile of forest 
land produces annually 441 tons of fixed carbon in the 
wood, {Comjjtcs Rendiu%) and Liebig increases the quantity 
to as much as 504 tons to the square mile. The same author 
also shows that all other vegetable i)roductions yield nearly 
the same quantity of carbon to the square mile. Now a prism 
of air extending to the upper limits of the atmosphere, and 
having a base of one square mile, contains 4,2G0 tons of car- 
bon, from which it results that the annual consumption of 
carbon by thrifty vegetation amounts to about one-nintli of 
all the carbon of the atmosphere which rests upon it. (Gas- 
parin; vol. ii.) 

From this it might at fii'st siglit appear that tlie carbonic 
acid of the air ought rapidly to diminish, and in a few years 
to be entirely exhausted ; but, as we liave seen, the carbon 
thus extracted is not lost to the air, but lent as it were to the 
organized matter of the globe ; for by the process of combus- 
tion and decay an equal amount of the same substance is 



-1859] WRITINGS OF JOSEPH HENRY. 165 

restored to supply the place of that previously abstracted, 
and the whole quantity of carbon in the atmosphere remains 
nearly the same from age to age, the measurable variations 
being only perceptible during the lapse of the ages which 
constitute a geological period. When we consider however 
the great amount of coal consumed at the present day in the 
mechanical arts and locomotion, it would appear that the 
amount of carbonic acid is increasing in the atmosphere ; 
but when we compare with this the improvements made in 
agriculture, and the stimulus thus afforded to the growth of 
plants and animals, the effects of these artificial conditions 
would apparently nearly balance each other. There is 
another source of abstraction of carbonic acid from the at- 
mosphere, namely, that which takes i)lacc thrbugli the agency 
of animal life in the production of coral ; but this again may 
be probably balanced by the carbonic acid emitted from the 
various active volcanoes of the globe. We do not however 
by these remarks attempt to establish the fact that in all 
parts of nature there is an exact compensation, and that our 
globe has always remained in the state in which it now exists, 
but that the great changes which affect our planet are ex- 
ceedingly gradual, and the conditions may be considered 
constant during the age of individuals, or even of nations. 

Should the carbonic acid of the air sensibly increase over 
the limits before mentioned, the vegetation of the earth would, 
as we have seen, become more luxuriant, and animal life de- 
generate into a lower type. If on the other hand, the car- 
bonic acid should be diminished, the reverse would proba- 
bly take place, vegetable life would become less, and animals 
would either correspondingly diminish in number, or they 
would assume a higher type. M. Flourens supposes that the 
amount of organic life on the surface of the globe has re- 
mained the same through all periods, though exhibited 
under different forms, but this would be dependent upon the 
permanency of the amount of organizing force from the sun. 

Saline matter in the a(m.os})here. — Air from the surface of 
the ocean contains a portion of the saline ingredients which 
in positions near the sea, and in some cases further inland, 



166 WRITINGS OP JOSEPH HENRY. [1855- 

produce a marked effect upon the character and condition of 
vegetation. Dr. Dalton found, at Manchester, one part of 
salt in one thousand parts of rain water. Brandes found in 
rain water, in Germany, besides common salt, chlorate of 
magnesia, sulphate of magnesia, carbonate of magnesia, chlo- 
rate of potassium, sulphate of lime, oxide of iron, oxide of 
magnesia, and salts of ammonia, the greatest part of these 
being ingredients of sea-water. This explains the fact that 
certain plants do not grow luxuriantly near the ocean unless 
screened by a fringe of trees or houses, or protected in some 
other way. Near the ocean, a number of garden plafits can- 
not be made to grow unless placed near a fence which inter- 
cepts the wind from the ocean. We might infer from this 
that the saline matter is carried mechanically by the air, 
and not diffused through it, as in tlie case of vapor. We are 
informed by Mr. Browne that a gentleman at Nahant has 
succeeded in raising pears to perfection by protecting the 
trees on the ocean side by a higli brick wall, perforated at 
intervals with comparatively small openings, sufficient how- 
ever to keep up the ventilation. 

Mineral matter in the atmospliere. — There is also constantly 
diffused tli rough the air a considerable quantity of mineral 
substances, in a state of impalpable powder. This is carried 
up by the ascending columns of air which are constantly 
rising under the varying heat of the different portions of 
the ground due to the influence of clouds and the various 
conditions of the surface, and is brought down in the rain 
which falls in the beginning of a shower. The presence of 
this material at all times, is rendered evident when a ray of 
light enters a small hole in the window shutter of a dark- 
ened room. By some, it has even been conceived tote an 
essential ingredient of the atmosphere. The amount of this 
is much greater than we might be led by casual observation 
to suppose. It falls upon the decks of vessels in mid-ocean, 
and forms dry clouds, which were observed by Prof. Piazzi 
Smyth, at the height of several thousand feet, upon the side 
of the Peak of Teneriffe. 



-1859] WRITINGS OF JOSEPH HENRY. 167 

Its constant presence in the atmosphere furnishes an ex- 
planation of the occurence of a minute quantity of mineral 
matter in the composition of certain plants which is not 
found in the soil in which they grow. 

PoUen of plants, — At certain seasons of the year, the pollen 
of the pine tree and other plants is carried to immense dis- 
tances, and after a thunder-storm is often found on the sur- 
face of water in our rain casks and from its yellow color is 
frequently mistaken for sulphur. 

Ozone, — Another substance which of late years has been 
discovered in the atmosphere by the indefatigable labors 
of Prof. Schonbein, the inventor of gun-cotton, is known by 
the name of "ozone," which is supposed from all the researches 
made upon it to be oxygen in a peculiar condition, in which 
its aflBnity for other substances or combining power is highly 
exalted. When a stream of frictional electricity is made to 
flow from the point of the prime conductor of an ordinary 
machine, a peculiar odor is perceived, due as is supposed to 
the oxygen of the air assuming an altered condition, and 
hence it has been inferred that ozone consists of oxygen with 
an extra dose of electricity. 

M. Clausius however has advanced another hypothesis 
which appears to be in accordance with other facts, namely, 
that an ordinary atom of oxygen, of which the atomic weight 
is eight, is in reality a molecule composed of two atoms, 
and that under the influence of electrical repulsion these 
atoms are separated, and in the unneutralized affinity, con- 
sequent upon this separation, the increased avidity of com- 
bination is evinced. 

Whatever be the nature of ozone, it is certain that it pos- 
sesses great powers of combination with many other sub- 
stances, and thus tends to produce chemical effects. It is 
probably produced on a large scale in the atmosphere, on 
the same principle by which it is obtained in the laboratory, 
namely, by the electrical discharge in the form of lightning 
from the clouds. 

The test for ozone consists of one part of iodide of potas- 
sium, ten parts of starch, and one hundred parts of water, 



168 WRITINGS OP JOSEPH HKNRY. [1855^ 

boiled together for a few minutes. A thin coating of this 
preparation applied to writing paper with a brush, being ox- 
posed to an atmosphere containing ozone, is rendered blue 
from the evolution of the iodine. In order to bring out the 
blue color distinctly, it is necessary to dip the paper in pure 
water. 

Besides the action of the electrical spark, ozone may be 
produced by the action of phosphorus on atmospheric air, 
provided moisture is present. It is also produced in the gas 
evolved in the galvanic decomposition of water. But by 
whatever process obtained, it always presents the following 
properties : 

First. It is a gaseous body of a very peculiar odor, ap- 
proaching that of chlorine when intense; when diluted, it 
cannot be distinguished from what is called the electrical 
odor. 

Second. Atmospheric air strongly charged with it renders 
respiration difficult, causes unpleasant sensations, and by its 
action on the mucous membrane produces catarrhal aflfec- 
tions. It soon kills small animals and undiluted must be 
highly deleterious to the animal economy. 

Third. It is insoluble in water. 

Fourth. It is a powerful electro-motive substance. 

Fifth. It discharges vegetable colors. 

Sixth. At common and even low temperatures it acts 
powerfully upon metals, producing the highest degree of ox- 
idization of which they are susceptible. 

Seventh. It destroys many hydrogenated gaseous com- 
pounds. 

Eighth. It produces oxidizing effects upon most organic 
substances. 

But the question of the greatest general interest regarding 
it is a physiological one. It is not found in places abound- 
ing in miasma, and from its energetic powers of combination 
it is thought to decompose the organic molecules of which 
this effluvium is supposed to consist, and hence observations 
in regard to it are highly desirable. 

Dr. Smallwoodi near Montreal, who has made an extended 



-1859] WRITINGS OF JOSEPH HENRY. IGO 

series of observations upon ozone, concludes that its presence 
in the air does not depend upon temperature but moisture. 
He has- observed traces of it when tlie thermometer was at 
20° F. below and at 80° above zero. But in general it was 
present in large quantities during the fall of rain and snow, 
which may account for its greater prevalence near the sea- 
shore than elsewhere. It appears to exist in great quantities 
in dew, and to this fact has been attributed the remarkable 
rusting eflTect produced on iron when exposed to this form 
of precipitation of water. 

Malaria, or miasma, — In certain places, there is diffused 
through the air an exceedingly minute quantity of a sub- 
stance which has a powerful effect on the human system, 
and frequently offers in such districts a serious obstacle to 
the cultivation of the soil. It is this which gives rise to in- 
termittent fevers and perhaps to maladies of a more malig- 
nant character. This substance is found in marshy and low 
places where animal and vegetable matter of an aqueous 
character is in a state of decomposition, but the winds which 
pass over these places transport the malarious effluvia to a 
distance and thus render whole tracts of country unhealthy. 

The corpuscules of this substance appear to adhere to the 
molecules of water, and are elevated with the latter by the 
ascending currents of air to heights which var}'^ in dif- 
ferent countries. Around the Pontine marshes, in Italy, 
the malaria disappears at the height of from seven hun- 
dred to one thousand feet, while in South America, accord- 
ing to Humboldt, it is found at an elevation of three 
thousand feet; usually however its effects are exhibited witli 
intensity at a much lower elevation than that first mentioned. 
It is also observed that humid air which transports miasma 
is deprived of this noxious material in passing through 
trees, and that in many cases, in the same neighborhood, a 
screen of foliage is sufficient to produce a marked difference 
between two places otherwise similarly situated. Double 
screens of fine gauze also placed in the windows of sleeping 
rooms answer a similar purpose, and should be resorted to in 
all cases as a precaution wherever there is danger of disease 



170 WRITINGS OF JOSEPH HENRY. [1855- 

from this cause. It is probable that the diffusion of malaria 
iu still air, as in the case of vapor, is exceedingly slow, and 
hence anything that tends to interrupt the current will much 
retard its transmission. It is asserted that in some cases 
near the focus of emanation it is less deleterious than at 
places at a considerable distance. It would appear from 
this to ascend vertically with the columns of heated air and 
to be afterwards wafted horizontally to a distance, and there 
impinging on the first elevation produces its effects; or per- 
haps this opinion has arisen from the screening influence of 
objects near the source. 

Miasma in perfectly dry air is in such small quantities as 
not only to be inaccessible to the investigation of science, 
but also insufficient to seriously affect human life. It is 
otherwise however in air cooled by the radiation of the even- 
ing and night. It appears then to be precipitated into the 
lower strata of the atmosphere with the mass of humidity 
with which it is probably connected, and when this is agaiji 
evaporated at sunrise, it carries up with it the miasma in 
its ascending movement. At this time it is taken into the 
system by swallowing, respiration, and possibly by absorp- 
tion through the pores of the skin, in sufficient quantities 
to manifest its deleterious effects. In malarious districts 
therefore caution should be taken against exposure to the 
evening precipitation and morning evaporation of the hu- 
midity of the atmosphere. Ground which has been a long 
time under water retains during a series of years the prop- 
erty of emitting the effluvia. The virgin soil in which decay- 
ing vegetable matter has accumulated for years, when first 
exposed to the action of the air by thq labor of the pioneer* 
gives off a large amount of malarious effluvia ; care should 
therefore be taken in the settlement of a new country not 
only to select a proper location, but also to protect the houses 
by a border of trees, particularly on the side against which 
the prevailing wind impinges. And it is to be regretted that 
good taste, as well as the comfort of an agreeable shade, does 
not more frequently induce the husbandman to spare some 
of the original products of the forest which are found near 



-1859] WRITINGS OF JOSEPH HENRY. 171 

the spot on which he erects hie dwelling. It is also stated 
that plants in active vegetation, as in the case of sunflowers, 
absorb deleterious eflBluvia ; but whether this effect is pro- 
duced independently of the screening we have mentioned 
has not yet been settled. In the fertile regions of the tropics 
where heat and moisture abound — for example, the valley 
of the Amazon — ^and where vegetation is luxuriant, the n^ala- 
rious effluvium is at its maximum ; while in dry countries 
with less vegetable life, such as those west of the Mississippi, 

it is not found. Nature thus is not indiscriminately benev- 
olent to civilized man ; in his uncivilized condition different 
races are confined to different districts, and the influences 
which affect one are inoperative on the other. It is only by 
investigating the causes of these differences, and thus in 
some cases arriving at the means of controlling them, that 
the civilized man becomes a citizen of the world, and within 
certain limits is enabled to overcome the natural enemies to 
which in his primitive ignorance he is exposed. 

The difficulty of investigating the nature of miasma has 
induced some to believe its effects due to variations of tem- 
perature and moisture ; but this is not sufficient to explain 
all the phenomena, as places very different in this respect 
vary greatly in their sanitary condition. The quantity of 
material (whatever it may be) which constitutes malaria is 
too minute to be immediately detected by the eudiometer, 
the instrument usually employed to analyze air. M. Moscati, 
in order to collect it in considerable quantities, employed a 
glass globe filled with ice, on the surface of which the aqueous 
vapor of the atmosphere was constantly precipitated. He 
found that the water thus collected in infected places was of 
a white color, inodorous, slightly alkaline, and after stand- 
ing a short time lime-water and acetate of lead produced in 
it a light precipitate. It contained animal matter, ammonia, 
and chlorate and carbonate of soda. The effect of this water 
upon animals has not (so far as we know) been tested, 
though it is said that sheep which feed upon grass covered 
by tlie morning dew in infected districts are subject to pecu- 
liar maladies. 



172 WRITINGS OF JOSEPH HENRY. [1855- 

The presence of organic matter may be detected in the 
process just described by dropping into the water a little sul- 
phuric acid and by afterwards evaporating the fluid we will 
obtain traces of carbon. If the experiment, for example, be 
made in a slaughter-house, comparatively a large amount of 
this substance will be obtained; and yet from abundant ob- 
servation it is known that the animal eflBluvia to which the 
butcher is constantly exposed are not of a morbific character, 
since the followers of this occupation are proverbially healthy. 
It would appear from this fact that the hurtful miasma is of 
vegetable not of animal origin. That collected by Regnault 
had the odor of burnt plants when incinerated. The same 
investigator asserts that a marehy odor does not always in- 
dicate feverish infection, and that in malarious districts it 
was above all to be feared at times when the air appeared 
pure and inodorous. From all the facts then, it appears 
most probable that the substance called miasma is an organi- 
zed body, endowed with life, and first generated in the de- 
composition of aquatic vegetation; that its introduction into 
the circulation of animals is a real innoculation affecting 
especially the nervous system; finally, that when it com- 
mences itself to decay in the open air it ceases to be dele- 
terious, though it gives rise to disagreciible odors. This in- 
vestigation opens a wide field for chemical research, to which 
the later improvements in the art of analysis may perhaps 
be successfully applied. Whatever may be the cause of the 
disease spoken of experience has indicated the following pre- 
cautions for those exposed to its influence: 

1st. In malarious districts, going out before the dew has 
evaporated, should be as much as possible avoided. 

2d. Before exposure to the morning air breakfast should 
be taken, or some slightly exciting drink, such as coffee or 
tea, rather than spirits. The former produces a healthful 
exhilaration, which prevents an attack of the miasma, while 
the re-action which succeeds the exhilarating effects of the 
latter tends to favor the absorption of the poison. 

3d. Flannel garments should be worn next to the body, as 
these tend to stimulate the skin and prevent the deleterious 
effect. 



-1859] WRITINGS OF JOSEPH HENRY. 173 

4th. The use of disinfectants, though perhaps less energetic 
in destroying miasma than in decomposing odors, should 
not be entirely neglected ; and for this purpose a small quan- 
tity of chloride of lime may be found beneficial. It is said 
that the flashing of gunpowder in a room answers the same 
purpose. 

5th. Screens of trees should be planted to interrupt the 
damp and warm wind from the focus of the emanation. 

6th. During warm weather, when ventilation is more nec- 
essary, the doors and windows should be provided with 
screens of fine gauze. 

7th. Boiled water should be used in preference to any 
other, or pure rain water, or that which has fallen some time 
after the rain commences, to which add a small portion of 
vinegar or acetic acid. 

8th. In cool evenings of summer, the dampness of the 
house should be dissipated by a blazing fire upon the hearth. 

It appears that the malarious influence is produced at a 
certain temperature, and that it is favored in marshy places 
by the heating of the water in shallow pools. It has been 
recommended to divide such places by deep par^illcl ditches 
or narrow canals at right angles to the direction of the i)re- 
vailing wind, the earth being thrown up on the side in the 
form of dykes, which are to be planted with rapidly growing 
trees or large shrubs. The ditch collects the water in too 
large bodies to be much heated, and this liability to become 
warmed is further lessened by the shade of the trees. The 
latter also serve as a series of screens to intercept any malaria 
which may arise. 

Nitric Acid. — If sparks of electricity are passed through a 
tube containing atmospheric air, the oxygen and nitrogen, 
which do not combine under ordinary circumstances, will 
chemically unite and form nitric acid. This union is sup- 
posed to bo the result of the production of ozonized oxygen, 
which promply unites with the nitrogen on account of its 
increased combining energy. The nitric acid thus formed 
combines with ammonia, which is also found in the atmos- 
phere as an original though a variable constituent, and forms 



174 



WRITINGS OF JOSEPH HENRY. [1855- 



nitrate of ammonia. To the atmosphere is also probably due 
the nitric acid which forms the nitrate of lime, from which the 
nitrate of potash, the principal ingredient of gunpowder, is 
produced in the soil containing the base. We have in this 
instance another confirmation of the conservation and trans- 
formation of power. The discharge of the electricity in the 
heavens expends a portion of its energy in producing a change 
in the condition of oxygen which in its turn attracts and 
imprisons (as it were) a portion of nitrogen — a substance 
which of all others, appears to possess the greatest repulsive 
energy, and the violent breaking loose again of this from its 
combination exhibits its power in the explosion which ensues. 
In this way the bolt of Jove may be said to be partly trans- 
formed into that of Mars, and the thunder of war to be but 
a reverberation of that of the heavens. 

Odors, — The observations which have been made during 
the photographic process have revealed the fact of the exis- 
tence in the air of the vapors of metals and other substances 
which though so minute as to have escaped particular 
attention are yet sufficient to interfere materially with the 
operations necessary to the production of perfect pictures. 
Almost all metals heated to redness give off effluvia percep- 
tible by the sense of smell. 

The diffusion in the air of the odoriferous principle 
of plants and other substances is a subject worthy of more 
attention than it has yet received. The wide diffusion 
of an almost infinitesimal quantity of matter in these cases 
may well excite our astonishment. A single grain of musk 
has been known to scent a room for twenty years, and 
without apparent reduction of the original material. To 
produce this result, the minuteness of the atoms must be 
beyond the conception of the imagination. From the in- 
fluence which chlorine has upon animal and vegetable odors, 
it is probable that hydrogen is an essential part of their com- 
position. The atmosphere itself, when pure, is inodorous; 
but the absence of perceptible odor may be due to the fact 
that our sense of smell ceases in some, cases to indicate an 
odor after having been for a certain time subjected to its in- 



1859] WRITINGS OF JOSEPH HENRY. 175 

fluence; for example, the nauseous effluvium which arises in 
some processes of the arts becomes often insensible to the 
operator, and the same may be said in regard to the effect of 
animal effluvia on the inmates of crowded and ill-ventilated 
houses. The sense of smell, like our moral faculties, thus 
becomes blunted by misuse or improper association. 

Matter in the aeriform condition is generally transparent, 
though diflTerent gases exhibit occasionally different colors; 
even the atmosphere possesses this property in a slight degree, 
as is evident in the fact of the slightly blue appearance of 
distant objects. 

From all that we have said, it appears that the aerial 
ocean, like the aqueous one, is a vast reservoir, principally 
composed of two ingredients of nearly constant proportions, 
and a number of adventitious materials which in some 
cases, though in very minute quantities, have a marked in- 
fluence on animal and vegetable life. There is however 
another variable ingredient, (previously alluded to in a 
general way,) which by its production and condensation, is 
the agent to which nearly all the fitful variations in our 
atmosphere are to be ascribed. I allude to the aqueous vapor 
of the atmosphere. But before proceeding to consider this, 
it will be necessary to treat more fully of some of the prin- 
ciples of heat and its influence on the climates of the earth. 

Maxima and Minima of Temperaiure. — A certain degree of 
heat is necessary to give mobility to the sap of plants, and 
this differs in each species of plant. Vegetation is acceler- 
ated and becomes luxuriant, provided it is furnished with a 
corresponding amount of humidity to compensate for the 
evaporation as we increase tlie quantity of heat. It is there- 
fore important to determine the average amount of heat in 
different places; but for this certain precautions are indis- 
pensable. It is not the direct heat of the sun that we at 
first wish to ascertain, but that of the air. Hence it is neces- 
sary to suspend the thermometer to a badly-conducting 
body, and the instrument itself should not have so great a 
volume as would prevent its readily taking the temperature 
of the atmosphere. If the bulb is large and tlie stem small, 



^*^> WKITIXGS OF JOSEPH HENRY. [1055- 

the degrees may readily be divided into small fractions; but 
iu this case the thermometer will fall behind in its indica- 
tions, since if the temperature be increasing, some time 
must elapse before the instrument can arrive at this new 
condition ; and in case it be falling, a similar tardiness will 
be exhibited. If on the other hand the bulb be very small, 
the degrees will be of less length ; but since there is little of 
the fluid to be heated or cooled, it will more readily take 
the temperature of the circumambient air. For determining 
however the mean temperature of a place, the thermometer 
should not be too small, since in that case it will be more 
easily affected by the heat of the body during observation, 
and at the same time it may be affected by an accidental or 
fitful stream of air, and thus give too high or too low an in- 
dication. One of the ordinary size iu which the bulb is 
about half an inch in diameter, is preferable. 

For a similar reason the thermometer ought not to be 
suspended in immediate contact with a large solid conduct- 
ing body, for example a stone or brick house, since this will 
retain the effects of a term of heat perhaps for several hours 
after the temperature of the air has changed. It should be 
suspended from an imperfectly conducting material, such as 
wood, and so situated that the air may circulate around it * 
on every side. It should also be screened from the direct 
radiation of the sun, and from the reflection of surrounding 
bodies; for if this be not done it will indicate the average 
of all the impressions received, and not simply the tempem- 
ture of the air. The thermometer therefore ought to be 
placed in the shade on the north side of the house, but a few 
feet above the level of the ground, in an unobstructed place; 
and indeed it has been recommended to suspend it between 
two large parallel horizonUil discs of wood, which will protect 
it from the earth below, the sky above, and every influence 
except that of the stratum of air in which it is situated. 
Instead of this however, we may enclose it in lattice-work, 
easily permeated by currents of air, and painted white on the 
outside to reflect back the more intense rays of heat which 
may accidentally reach it. 



-1859] WRITINGS OP JOSEPH HENEY. 177 

If our instruments consist of a maximum and a minimum 
self-roistering thermometer, exposed to the air in the way 
we have indicated, it will be sufficient in order to obtain the 
average temperature of the day approximately, to note the 
temperature of each butonce in twenty-four hours. If we then 
add together the maximum and minimum, and divide the 
sum by two we shall have approximately the average tem- 
perature; but this is not precisely the quantity required for 
meteorological and agricultural purposes, or that which en- 
ables us to judge of the heat of different days or different 
periods, since the thermometer may at different times of the 
day be suddenly elevated or depressed and not reach its 
maximum and minimum gradually, as is usually the case. 

To determine these points with more precision, and the 
average temperature of the air during the day, we must ob- 
serve the thermometer at very short intervals; for example 
every quarter of an hour. If we add these into one sum 
and divide by ninety-six we shall have the mean or average 
temperature of the day. Before division however caution 
is to be observed in combining the observations taken in 
winter, or when the temperature sinks below zero, to subtract 
the sum of the observations with the minus signs from the 
sum of those with plus signs. 

In running our eye down the column of a series of obser- 
vations of this kind, we can mark not only the maximum 
and minimum temperature for the day, but also the time 
at which they occurred. If we continue these observations, 
during the month of thirty days for example, we shall obtain 
thirty maxima and as many minima, and an equal number 
of mean temperatures. If we now add these thirty observa- 
tions of the same kind together, and divide by the number 
tliirty, we shall obtain the maximum, the minimum, and the 
mean of the month. Similar observations continued through- 
out the year and thus combined will give us the mean of all 
the maxima, of all the minima, as well as the general means 
of all the three hundred and sixty-five or three hundred and 
sixty-six days of which the year may be composed. 

There is still another way of combining these observa- 

12-2 



178 WRITINGS OF JOSEPH HENRY. [1855- 

tions. We may take, for example, the mean of all the tem- 
peratures of mid-day for the month or the year, or of any other 
hour of the twenty -four, and from this obtain the mean tem- 
perature of all hours of the day and night. Finally, instead 
of limiting our observations to a single year we may extend 
them to a series of years, in order to determine more ac- 
curately the mean temperature of a given place, all acci- 
dental variations of particular years and seasons being reason- 
ably supposed to balance each other. It is by this admira- 
ble invention of extended averages that order and regularity 
are deduced from phenomena which appear to be under the 
influence of no fixed laws, and that we are enabled to arrive 
at permanent and constant quantities, by eliminating those 
which are irregular and variable. 

A series of observations continued during the day and 
night through a number of years, or even a single year, in- 
volves an amount of labor which few men of science can 
aflford to bestow upon meteorology; and few have the indus- 
try and perseverance necessary to so prolonged and tedious 
an effort. This task however has been performed under the 
direction of several persons in this countr}', namely. Prof. 
Dewey, in Massachusetts; Capt. Mordecai, at the Unit^ 
States Arsenal, near Philadelphia; Prof. Bache, atGirard Col- 
lege, Philadelphia; Prof. Snell,at Amherst; and Col. Lefroy 
of Toronto ; not to mention the names of a large number of 
persons who have executed the same work in Europe. 
Could it be repeated in a number of different places in this 
country, the results would be of essential importance in 
correcting the ordinary observations made at fixed hours of 
the day. 

To illustrate these observations and the uses to which they 
may be applied, we shall select a series made since 1816, at 
the Observatory of Paris, by M. Bouvard, at six different 
epochs of the day, namely, from nine o'clock till mid-day, 
and from three to nine in the evening, the other hours be- 
ing given by interpolation : 



-1859] 



WRITINGS OF JOSEPH HENRY. 



179 



Hours. 


Temperature. 


Hours. 


Temperature. 




OC. 


op 




OC. 


op 


Midnight. 


8-6 


47-80 


1 P. M. 


141 


57-88 


1 A. M. 


81 


46-58 


2 


14-47 max. 


5805 


2 


7-7 


45-86 


8 


18-91 


57-04 


8 


7-4 


45-82 


4 


18-4 


5612 


4 


7*18 min. 


44-88 


5 


12-8 


5504 


5 


7-6 


45-60 


6 


12-2 


58-96 


6 


8-2 


46-76 


7 


11-6 


52-88 


7 


9-2 


48-56 


8 


10-8 


51-44 


8 


10-8 


50-54 


81 


10-67 mean. 


51-21 


Bi 


10-67 mean. 


51-21 


9 


1019 


50-84 


9 


11-21 


5218 


10 


9-7 


49-46 


10 


121 


58-78 . 


11 


9-1 


48-88 


11 


12*9 


55-9!?! 








Noon. 


18-5 


56-80 


Mean 


10-67 


51-21 



From this table we. see, first, that the annual mean tem- 
perature at Paris is 10°-67 C, or 51°-21 F. Second, that the 
minimum is near four o'clock a. m., and the maximum 
about two o'clock p. m. Thirdly, which follows from the 
last, the air is heated during ten consecutive hours, and is 
cooled during fourteen hours. Fourth, that we fall into a 
small error in deducing the mean temperature from the max- 
imum and minimum of the day, the true mean being 10°'67; 
while the other is 10°'8. Fifth, that the mean temperature 
is at 8 h. 20 min. in the morning and 8 h. 20 min. in the 
evening. From this it is evident that, in order to find the 
mean temperature of the year, it is sufficient to observe the 
thermometer each day at twenty minutes past eight in the 
morning and at twenty minutes past eight in the evening; 
but if our object is to obtain the mean for each month of 
the year, it is necessary to change tlie hour in question, 
since it is found that for January, 1 o'clock a. m. is the proper 
hour, for July, 7 o'clock a. m. ; and for all the other months, 
intermediate hours. The epoch of the mean experiences 
simihir changes in the evening. 

Having discussed the variations of the temperature of 
different hours, it now remains to speak of the monthly va- 
riations. From twenty years' observations at Providence, 
Rhode Island, the following result has been obtained by 



180 



WRITINGS OF JOSEPH HENRY. 



[18S5- 



Profes3or Caswell, of Brown University. This gentleman 
has made a series of observations extending through upward 
of a quarter of a century, and has presented the whole to the 
Smithsonian Institution for publication. 

Tanperatare of Providenee, Rhode Island; by Prof, A. O^aWBLL. 





Month*. 


1 


Teais. 




Jsn. 


Feb. 


- 


Apr 


M-> 


Jun 


JulJAug 


Sep 


Oct 


Nov 


Dee 


1838.. 


;;; 


17-0 


S5-i 


40-8 


58-5 


M-2 


r5-O|71-0 


Ul-4 


47-S 


86-8 


25-8 


470 


1839 - 


26-3 


27-0 34-0 


48-7[-W-0'fl2-2 


71 -7 167-9 


61-1 


51-5 


37'8 


30-6 


47-8 


1810 


Ifl-fi 






72-2 70-0 


58-5 


51-8 


B9'2 


27-7 


488 


1B41 - 


:ii>'.'. ■.■-. 1 ;■. 1 ':■■:. -■>■] <■- .; -■mi «9.2 


B3-2 


45-8 


liV-3 


32-7 


47-8 


1842 




5»3 


BO-9 


38-T 


802 


49-0 


1843 


::i-j .■■ i '.-■:■■ .i 1 ! . .- ^ (iO-B 


61-3 


4B-3 


37-e 


ao-B 


47-2 


1844 


iQ--2 ■■■■•2 :;...: --.f .. --.- .-. ..-1 .. ..^ J fi7-8 


50-G 


49-9 


se-i 


B2-2 


47-9 


1845 


30'7 


!;8-5 


41 3 


44 -C 


y--* 


14'8<iOO|08>2 


57-5 


60-7 


426 


240 


48-1 


1848 


27-8 


fel-7 


B9-4 


46 8 


53-2 


BO-7 


6T'5 


71-2 


86-0 


50-2 


44-6 


29-8 


48-2 


1847 


20-3 


28-7 


32-3 


43 


.. 


eG-6 


n.s 


68-7 


62-S 


.... 


45-6 


noa 


402 


Mean of 10 










— 









— 








y^i*" 


280 


26-8 


sa-n 


453 


». 


85-1 


70'6 


60-3 


61-0 


'•■' 


«• 


30-4 


481 


1848. 


3 3 


4 


m 


■1 H 









14 




,. 


37 8 


87 3 




500 


1840. 


"4 flS 


47 3 


312 


483 


1850- _ 




486 


293 


48-8 


1851. 




60 


>6 5 


48-5 


1852. _ 




i 


83- 


37 8 


48-8 


1853. _ 


B i 


i 4 


426 


286 


48-0 


1864. 


20 4 


^t 




uU 


52 9 


407 


id, 


47-9 


1850 


300 


211 


79 


Bl« 


52 4 


420 


82 S 


481 


1856- _ 


IB 3 


227 


>e 


68 2 


^2 


89 4 


2S6 


46-6 


1867. _ 


16 3 


82 7 


3 








8 


608 


o05 


42 3 


346 


46-8 


ileaa of 10 































'3 I 


7j 


33 


"' 


^4 


61 


71 C 


94 


14 


1 7 


412 


309 


48-S 


Meun of 20 




























yen« 


27-1 


27-1 


34-0 


44. 


55-2 


60-6 


71-0 


09-3 


Rl-2 


50-7 


40-6 


30-6 


48-2 



It appears from tliis tabic that the coldest month is Janu- 
ary, and the warmest are July and August, which are nearly 
the same, Tlie mean temperatures of April and October are 
nearest to the mean of the year. In the two periods of ten 
years each, at Providence, the difference between the mean 
temperatures is but two-tenths of a degree ; the differences 
also between tUe mean temperatures of the several months 



-1859] WKITINGS OP JOSEPH HENRY. 181 

in the two decades scarcely differ a degree in the whole 
series. If the times were further extended the agreements 
would probably be closer, the instruments remaining the 
same. These facts illustrate the truth of what we have pre- 
viously said relative to the deduction of definite results from 
the most complex and variable elements, and the perman- 
ency of the mean temperature of a given position ; the sum 
of the variations consisting in oscillations on either side of 
the mean, which in the aggregate neutralize each other. 

It is known from extended observation that the same 
weather exists at the same time over a large extent of country. 
For example, during a cold winter, it is comparatively cold 
over the whole of France; and in the State of New York, 
though the temperature be diflFerent in diflFerent places, a 
cold January will be cold over the whole state; hence a table 
carefully made at any one place will serve to indicate the 
relative temperature of others in the same district. 

We see from the foregoing table that the greatest heat of 
the day at Paris happens at 2 o'clock, while we know that 
the solar rays are most intense at 12 o'clock. We have in 
a previous report given an explanation of this phenomenon, 
namely, that the earth is constantly radiating heat into space 
and receiving it from the sun the whole time it is above the 
horizon; the temperature therefore will constantly increase 
while the amount of heat received is greater than that given 
off. The greatest amount of heat received in a minute is at 
12 o'clock, and hence the increase of temperature at this 
time will be the greatest; but the earth after 12 o'clock still 
continues to receive more heat than it gives oflF, and hence 
the temperature of the air will still continue to increase, 
though at a less rapid rate, until about 3 o'clock in our lati- 
tude. The radiation into space from the earth and the absorp- 
tion from the sun about balance each other, and the tem- 
perature will then remain stationary at its maximum point 
during some time, the loss and gain being equal. After this 
the loss is greater than the gain, and this goes on continually 
until the setting of the sun, when the radiation is entirely 
uncompensated and cooling takes place, at first with a sudden 



182 WRITINGS OP JOSEPH HKNRY. [1855- 

accelerated velocity, and then gradually diminishes in in- 
tensity until daylight, when the earth has> arrived at the 
minimum of temperature. After this, again, the earth begins 
to receive more heat than it loses, and the temperature of 
the air constantly rises again until 3 o'clock. If the earth 
were to radiate heat as rapidly at night as it does in the 
day the minimum temperature would be at about 9 o'clock 
in the morning; but on account of the diminished radiation 
with diminished temperature, the compensation takes place 
about the rising of the sun. When the radiation towards 
the sky is prevented by a transparent covering which admits 
the radiation from the sun, as in the case of a house lighted 
by windows in the roof, the maximum temperature takes 
place at a much later period of the day; and indeed were 
the radiation to the sky entirely stopped the temperature of 
the earth would increase indefinitely. 

Temperatures below the surface. — At a certain depth below 
the surface of the earth there is a stratum of invariable tem- 
perature, the depth of which augments with the latitude, 
and in our climate is from about 100 to 115 feet. In general 
the temperature of this stratum appears to be a little more 
elevated than the mean annual temperature of the surface, 
and this excess appears to increase with the latitude. This 
stratum, it is evident, cannot be a reguhir surface, since it 
must necessarily partake in a considerable degree of the varj^- 
ing contour of the external surface of the earth. The first 
observations which were made upon this subject were in the 
cellars of the Observatory at Paris, at the depth of 67J feet 
below the surface. Tliey extend over a period of more than 
fifty years, and show an invariable temperature of 53°*28 F. 
The thermometer used in these observations was a most 
delicate one, constructed by Lavoisier, and it in no instance 
showed a variation of one-tenth of a degree Fahrenheit above 
or below 53°'28; and even these variations, small as they 
are have been traced to accidental causes. 

Below the surface of the ground, and at a depth of from 65 
to 80 feet, but few ol)servations have been made, and these 
have been principally applicable to the middle latitudes of 



-1859] WKITINGS OP JOSEPH HENRY. 183 

the northern hemisphere. From all the observations Pouil- 
let gives the following deductions : 

1. The diurnal variations are not perceptible at depths 
greater than about 40 inches. 

2. The mean annual temperature of the different strata 
differs little from the mean annual temperature of the air. 

3. The differences between the maxima and minima of 
tlie different strata decrease in a geometrical progression, 
while the depths increase in an arithmetical progression. 

4. From all the observations it appears that at a depth 
of from 26 to 29 feet, the annual variation is only 1°*8 F; at 
from 49 to 52 feet, it is but 0°'18 F. ; and at a depth of from 
65 to 81 feet, it becomes only 0^-02 F. 

5. At the depth of about 26 feet, or where the variation is 
2® F., the seasons are precisely reversed ; that is, the maxi- 
mum temperature occurs about the 1st of January, and the 
minimum about the end of June. 

Effed of heal on plants, — We have stated that all the trans- 
formations of matter going on around us, the power exhib- 
ited in the growth of the plants, in the functions and motions 
of animals as well as in the winds, — are referable to im- 
pulses received from the sun; but the mere continuance of 
the heat of a body at a certain temperature does not produce 
a continuous change in it; for example, a piece of metal, 
when kept at the same temperature, may remain unchanged 
for years, provided the intensity of the heat is not sufficient 
to melt it. In order therefore that heat may do work, or 
effect a permanent change in matter, it is necessary that it 
be applied by means of some mechanical arrangement anal- 
ogous to a machine. In most cases, an intermediate agent 
(such as steam or heated air) is employed in connection with 
the machinery, and we have a striking natural arrangement 
of this kind in the organization of the plant. If the stem of 
a plant were solid, and did not consist of minute colls filled 
with evaporable liquid, the heat of the atmosphere, so long 
as it were constant, could produce no change. To under- 
stand this, let us suppose a tube of glass with a minute bore 
(for instance the tube of a broken thermometer) to Iiave 



184 WRITINGS OF JOSEPH HENRY. [1855- 

its lower end placed in water, the liquid will rise perhaps to 
an inch above the general level of the liquid in the vessel, 
and. here it will remain. The cause of this ascent is the at- 
traction of the glass for the liquid and the liquid for itself, 
and is familiarly known under the name of capillarity. A 
perpetual flow of water can never be produced by this action 
since if we cut oflf the tube before-mentioned, leaving but 
three-fourths of an inch above the water, the attraction of the 
glass will draw the liquid up to the very top, but will not 
permit it to run over, because the same attraction which sus- 
pends it will prevent it from overflowing. The atom of 
water at the top of the tube will be attracted as much down- 
ward by the glass as the next one below will be attracted 
upwards; hence an equilibrium will ensue. 

If however we apply heat to the upper surface, which will 
evaporate the water, a new portion will be drawn up to re- 
store the equilibrium ; and if this process be continued, a con- 
stant current will be maintained, and a definite amount of 
mechanical work will be performed. If the liquid xjontain 
diflerent substances in solution, these will be retained, it may 
be in a solid form, jand in this way a solid substance may 
be brought up and deposited at the end of the tube. If across 
the lower end of the tube a porous membrane be stretched, 
and if the liquids above this, and that in the vessel below, 
be of a diflerent quality, which would necessarily result on 
account of the evaporation mentioned-, then the ascensional 
power would be very much increased by the process called 
endosmose. Without considering at present this action very 
minutely, we may apply the principles we have here given 
to the means by which heat becomes a motive power in build- 
ing up a plant. The stem of a tree is an arrangement anal- 
ogous to an assemblage of minute tubes, such as we have 
described, terminating in leaves above, from the surface of 
which constant evaporation is going on, and a current of 
liquid ascending called crude sap, which consists of water 
containing in solution the various substances imbibed by the 
roots, and elaborated by the leaves. The tubes are not con- 
tinuous, but are elongated cells analogous to a glass tube, the 
ends of which are closed with porous membrane. 



-1859] WRITINGS OF JOSBPH HENRY. 185 

We can scarcely, doubt that by this arrangement the mo- 
tive power which gives rise to the circulation of the sap is 
the heat derived from the atmosphere and the direct rays of 
the sun. But a small part however of the material of which 
the plant is mainly built up, (namely carbon) is elevated from 
the roots. This is furnished, as we have before stated, by 
the de-composition of the carbonic acid absorbed from tlie 
atmosphere into the pores of the leaves, and there resolved 
by the chemical .ray of the sun. It is at this place that the 
liquid brought up by evaporation is elaborated into true sap, 
under the principle of vitality, which being carried down- 
ward through the cells by endosmose, serves by secretion 
to build up new cells, and thus to increase every part of 
the pliant. The rapidity of evaporation will depend, the 
amount of heat being the same, upon the quantity of vapor 
already in the atmosphere ; and hence with the same de- 
gree of temperature the amount of work performed would 
appear to be greater in a dry than in a moist atmosphere; 
but since the carbonic acid which is decomposed is probably 
absorbed by the water in the leaf, too rapid an evaporation 
will retard rather than increase the useful eflfect. 

But little is known of the minutiae of this process, or how 
far the results may be influenced by other causes than those 
actually observed. We are assured however by observation, 
that beyond a certain degree of heat, a given .plant cannot 
have a healthy condition, and also below a certain tempera- 
ture, which is still above freezing, the sap of plants ceases to 
have an active if any circulation. 

HeaJt necessary for the growth of plants, — ^The hypothesis was 
early advanced that for each plant a certain amount of heat 
is requisite in order to its developement from one stage of 
growth to another; for example, in the case of wheat j from the 
time it begins to sprout until it arrives at its full maturity, 
a definite quantity of heat is required, other conditions be- 
ing the same, though the time in which it may be furnished 
may be different in diflerent instances. DiSerent methods 
however have been proposed for estimating this heat. Reau- 
mur, who first advanced the hypothesis of the definite amount 



186 WRITINGS OF JOSEPH HENRY. [1855- 

of heat, as well as late writers on the subject, has proposed to 
calculate it by multiplyiug the number of days in which 
the plant is passing through its growth by the mean tem- 
perature of each day ; while M. Quetelet, of Brussels, who 
has made more experiments on this subject than any other 
person, thinks that the heat ought to be measured, not by 
the simple product of the sum of the temperatures of the 
several days but by the sum of the squares of the tempera- 
tures of these days. He deduces this rule from the consider- 
ation that if hjeat be due to vibration, the impulses from 
it ought to do work in proportion to the square of the inten- 
sity, and not simply in proportion to the intensity. For ex- 
ample, a cannon ball moving with twice the velocity will 
peuetratea wall four times as far, — moving with three times 
the velocity, nine times as far, — ^and so on, in proportion to 
the square of the velocity. In accordance with this, let 8 
represent the amount of heat required to produce the full 
development of the plant, and t and t' be the mean tempera- 
tures of the several days; then will S={tf + {tj + (<")«, &c. 
It follows as a consequence of the law of the square of tem- 
peratures that alternation of temperatures within certain 
limits may produce greater effect than a uniform tempera- 
ture. For example, if on three consecutive days the tempe- 
ratures were 70°, 60°, and 80° F., and on three other days, 
70°, 70°, 70°, though the average heat is the same, the effect 
of the former will be slightly greater than that of the latter; 
since the sum of the squares of the first is 14,900 while that 
of the latter is 14,700. 

From a priori considerations there can be no doubt that 
to produce a given amount of organization a definite amount 
of power must be expended ; but we are unable to say in, the 
present state of science how much of the power which may 
disappear is lost in producing other than useful eflFects. Also, 
in the foregoing investigation it might reasonably be sup- 
posed that the mean heat of the day, in part, should be de- 
rived from the heat of the sun, and not alone from that of 
the air. The upper surface of a plant will be heated by the 
direct rays of the sun, while the lower will- be exposed in the 
shade to the heat of the air. It has therefore been proposed 



-1859] WRITINGS OP JOSEPH HENRY. 187 

to employ the temperature obtained from the mean of the 
observed thermometer in the sun and in the shade during 
the day. To render this principle of use in practice, a series 
of observations in different seasons of the year, on the tem- 
peratures of thermometers in the sun and in the shade would 
be necessary. Besides this, since vegetation is comparatively 
but little advanced at night, the length of the day should be 
taken into account, which in the neighborhood of the equa- 
tor is 12 hours, and in the vicinity of the polar circle, nearly 
24 hours. Another correction is necessary in order to obtain 
strictly comparative results, namely, that which is due to the 
fact that different plants begin to show signs of vitality in the 
spring at different temperatures. 

Allowing the truth of the proposition of the definite 
amount of heat required for the full development of each 
plant, we have a ready explanation of the fact that some 
grain will come to maturity in climates of very different tem- 
peratures, the less intensity of heat being compensated for 
by the longer duration of the day. Though each species of 
plant may require a definite amount of heat for its perfect 
maturity, yet this is by no means the measure of the power 
expended in the organization, though it may bear a definite 
ratio to it. The chemical ray of the sun decomposes carbonic 
acid, and thus furnishes tho greater part of the material of 
which the plant is composed, and in the process of germ- 
ination and assimilation, probably furnishes a portion of the 
power necessary to carry on these processes. 

The following table is selected from the memoirs of M. 
Quetelet, of Belgium, and contains the times of leafing, blos- 
soming, and fructification of plants found in this country as 
well as in Europe. The selection has been made at my re- 
quest by Dr. L. D. Gale, of Washington, and it is hoped that 
the times will be compared with those pertaining to the same 
periods of the developments of the same plants in different 
parts of this country. 

The observations from which the original table was con- 
structed were made in the garden of the Royal Observatory, 
at Brussels, and according to the author, they may be ap- 



188 



WRITINGS OF JOSEPH HENRT. 



[1855^ 



plied not only to Belgium but also to the whole of Europe, 
due regard being had to the diflFerences of latitude and ele- 
vation between Brussels and other places. The correction 
for each degree of latitude is four days for each degree, to be 
added or subtracted accordingly as the place is to the north or 
south of Brussels. The correction for elevation is a retard- 
ation also of four days for every 330 feet above Brussels, 
which is itself about 195 feet above the level of the sea. It 
must be understood that these corrections are only approx- 
imate, for we are obliged to abstract the consideration of the 
nature of the soil, the exposure of the plant, and the more 
or less continental lodiality, that is the greater or less dis- 
tance from the sea. 

Plants that grow in Europe and in the United States j whether indigenous or 
introduced — experiment continued ten years ; by M. Qtjstelsi*, of Brussels. 



KAMKS OF PLANTS. {Time of leafing.)* 



Acer peudo-platanuB, a maple 

.^culus hippocastanum, horse chestnut. 

Amygdalus Persica, peach — 

Berberis vulgaris, barberry 

Betula alba, white birch 

Bignonia catalpa, catalpa tree 

Crataegus oxyacantha, English hawthorn. 

Clematis viticella, Italian clematis 

Daphne mezereuin 

Fraxinus nigra, black ash 

Gleditschia rerox, honey-locust tree 

Juglans nigra, black walnut 

LoniceraTartarica, Tartarian honeysuckle 
Magnolia grandiflora, gr. flower magnolia 

Moms alba, white mulberry _...» 

Philadelphus coronarus, mock orange — 

Populus alba, white poplar 

Populus balsamifera, balm of Gilead 

Prunus cerasus, cherry laurel 

Prunus domestica, common plum 

Prunus spinosa, sloe, black tnorn 

Pyrus communis, common pear 

Pyrus malus, apple 

Enus typhina, staghom, sumach 

Ribes grossularia, gooseberry 

Eibcs rubrum, red currant 

Kibes nigrum, black currant 

Eobinia pseudo-acacia, white locust 

Sorbus aucuparia, mountain ash 

Tilia Europoea, European linden tree 



Meantime. 


Earliest. 


April 20 


April 7 
March 27 


April 6 
March 28 


March 4 


March 22 


Feb. 26 


April 9 
May 1 


March 27 


April 17 


March 23 


Feb. 26 


March 25 


Feb. 23 


March 18 


Feb. 28 


April 26 


April 16 


May 9 


April 30 


April 28 


April 19 


March 6 


Jan. 80 


April 19 
May, 2 


April 4 


April 21 


March 18 


Feb. 23 


April 12 


April 1 


April 5 


March 14 


April 6 


March 27 


April 2 


March 6 


April 1 
March 30 


March 1 


March 10 


March 30 


March 12 


April 19 


April 1 


March 8 


Feb. 18 


March 17 


Fob. 25 


March 17 


Feb. 24 


April 23 


April 9 


April 7 


March 18 


April 7 


March 18 



Latest. 



4 

5 

26 

10 

5 



April 28 

April 27 

April 19 

April 14 

April 20 

May 19 

April 16 

April 20 
April 
May 
May 
May 
April 

April 29 

May 15 

April 18 

May 1 

April 22 

April 21 

April 28 

April 28 

April 22 

April 20 
May 
April 
April 
April 
May 

April 21 

April 22 



7 
3 
8 
8 
10 



* Latitude of Brussels. 



-1859] 



WRITINGS OP JOSEPH HENEY. 



189 



Table of Plants — Continued. 



KAICKS OF PLANTS. (Time of flowering,) 



Acer pseudo-platanusi a maple 

Achillea millefolium, yarrow 

Aconitum napellus, monkshood 

• iEisculuB hippocastanum, horse chestnut. 

Amygdalus f eisica, pench — 

Amorpha fhiticosa, common false indigo 

Anthemis cotula, mayweed 

Berberis vulgaris, barberry 

Betula alba, white birch 

Crataegus oxyacantha, English hawthorn. 

Clematis viticella, Italian clematis 

Daphne mezereum 

Lonicera Tartarica, Tartarian honeysuckle 
Magnolia grandiflora, cr. flower magnolia 

Horns alba, white mulberry 

Philadelphus coronarius, mock orange 

Populus alba, white poplar 

Populus balsamifera, balm of Gilead 

Prunus cerasus, cherry laurel 

Prunus domestica, common plum 

Prunus spinoea, sloe, black thorn 

Pyrus communis, pear tree 

Pyrus malus, apple 

Rhus typhina, sumach • 

Ribes grossularia, gooseberry 

Ribes rubrum, red currant 

Ribes nigrum, black currant 

Robinia pseudo-acacia, white locust 

Sorbus aucuparia, mountain ash 

Tilia Europsea, linden tree 



Mean time. 



April 28 

July 13 

June 1 

May 3 
March 20 

June 12 

June 5 

May 4 

April 8 

May 4 

June 29 
March 15 

May 9 

April 16 

May 22 

May 23 

March 23 

March 23 

April 16 

April 16 

April 7 

April 13 

April 25 

July 13 

April 3 

April 2 

April 14 

May 30 

May 2 

Juno 9 



Earliest. 



April 19 
July 5 
May 15 
April 23 
Feb. 27 
May 28 
May 6 
April 18 
March 22 
April 16 
June 2 
March 3 
April 23 
March 8 
May 15 
May 11 
Feb. 28 
Feb. 28 
April 2 
March 27 
March 2 
March 9 
April 12 
July 5 
March 12 
March 18 
March 28 
Mav 17 
April 16 
May 15 



NAMES OF PLANTS. {Time of fruit.) 



Acer pseudo-platanus, a maple 

Amygdalus Persica, peach 

Prunus cerasus, cherry laurel 

Pyrus communis, common pear — 

Ribes grossularia, gooseberry 

Ribes rubrum, red currant 

Ribes nigrum, black currant 



Meantime. 



Oct. 

Aug. 

June 

Aug. 

June 

June 

June 



30 
22 
11 
26 
25 
15 
15 



Earliest. 



Oct. 

Aug. 

May 

July 

Juno 

Juno 

June 



25 

5 

30 

28 

16 

6 

8 



Latest. 



May 


10 


July 


30 


June 


12 


May 


16 


April 


8 


June 


24 


June 


19 


May 


20 


April 


22 


May 


23 


July 


14 


April 


2 


May 


23 


April 


25 


June 


3 


Juno 


4 


April 


20 


April 


20 


May 


4 


May 


3 


April 


80 


May 


2 


May 


8 


July 


25 


April 


22 


April 


22 


April 


30 


Juno 


12 


May 


15 



Juno 17 



Latest. 



Nov. 
Sept. 
June 
Sept. 
July 
June 
June 



3 
11 
24 
14 

8 
29 
27 



Ileai on differerU surfaces, — ^The amount of heat which falls 
upon a given surface depends upon the inclination to the 
diflferent points of the horizon. A field, for instance, in our 
latitude sloping towards the south, receives a greater, and 
one towards the north a less amount of heat; moreover, the 
former obtains more than an equal extent of ground parallel 



190 WRITINGS OF JOSEPH HENRY. [1855- 

to the horizon, and the latter, as in the other case, much less. 
A field also which slopes in an easterly direction receives less 
heat than another inclined towards the west, inasmuch as 
more reaches the latter, since the maximum heat of the day 
takes place after the sun has passed the meridian; as it is, 
each of these enclosures gets a less amount than one of equal 
extent parallel to the horizon. 

Estimate of temperature by rings in trees. — It frequently hap- 
pens that permanent records are found of the past condition 
of our globe in the impressions retained in the rocky strata, 
and that the yearly occurrences of certain phenomena such 
as the annual deposit from the overflowing of rivers. Such 
records may be rendered available in determining the time 
of actions which may have long since ceased, or which con- 
tinue to the present day. It is well known that the trees 
of our latitude increase in size by the deposition of an addi- 
tional layer annually between the wood and the bark, and that 
a transverse section of such a tree presents a series of concen- 
tric though irregular rings, the number of which indicates 
the age of the tree. The relative thickness of these rings de- 
pends on the more or less flourishing state of the plant in the 
year in which they were formed, and therefore indicates the 
relative state of heat and moisture during the same period. 
Furthermore each ring in some trees may be observed to be 
subdivided into others during the same year, indicating that 
the vegetation was advanced or checked at intervals during 
the season. Furthermore it has been found by observation 
that even the motion imparted to a tree by the wind has an 
influence on its growth, giving to its trunk an oval form, the 
longer direction of which will be that of the prevailing wind. 
A thin slice therefore cut from a large tree at right angles to 
its axis, carefully polished and varnished, forms a natural 
record of the weather well calculated to call forth admiration 
and to impart instruction. It is scarcely necessary to remark 
that the year should be carefully identified, corresponding 
to a given circle, in order that the whole might be properly 
numbered. 

Mr. Babbage has proposed an ingenious application of this 



-1859] WRITINGS OF JOSEPH HENRY. 101 

principle for carrying back the series of records by means of 
trees which arc found in the deep bogs of different parts of 
Great Britain. By searching for corresponding thick or 
thin rings in the outer circumference of one tree and in the 
inner of another, a number of trees may be arranged in a 
series, and thus the record extended back into the geological 
periods. Whatever may be the practical value of this plan, 
it is certainly ingenious and worthy of attention. Since the 
trees found in bogs are, wq may suppose, the regular and 
consecutive productions of the primitive forests, they would 
probably represent the successive vegetation of a series of 
centuries. 

The remains of plants found in the rocky strata indicate 
that the same diversity of weather and the same changes of 
seasons existed in the past geological ages as at the present 
time. By carefully studying the rain marks on sandstone, 
the direction of the wind during storms in the ancient periods 
maybe determined; and this will probably be found the 
same as in thunder showers of the present day. The remains 
of plants and animals of a tropical character found abun- 
dantly in the northern regions assure us that the tempera- 
ture of the surface of the whole globe has undergone remark- 
able changes. 

Effect of different surfaces. — The rays of heat from the sun 
which strike the earth are partly reflected into space and 
partly absorbed by the surface in producing an elevation of 
temperature. The absorbent and reflective powers arc com- 
plementary to each other, and vary greatly in different sub- 
stances, and as we have seen according to their color and 
texture. Lampblack possesses this power of absorption in 
the greatest degree; and if we represent this by 100, that of 
common glass will be 90, and that of polished metallic sur- 
faces about 6. Consequently, the latter have a high reflec- 
tive power, while that of lampblack and other dark sub- 
stances is very small. This is a matter of interest to the 
agriculturist, since the amount of heat which may be re- 
ceived by a given surface will depend very much upon its 
color; and indeed in some cases, charcoal or other dark sub- 



192 



WRITINGS OF JOSEPH HENRY. 



[1855- 



stance has been strewed over the ground to increase its ab- 
sorbtive power. 

The following table by M. Schubler is copied from Bec- 
quorel, and gives the greatest elevation of temperature ob- 
tained by different soils exposed to the direct rays of the sun, 
while the surrounding air was at about 78®. 

AfaxtiNiim of temperatures of rarious earths exposed to tlte sun, by ScHUBLER. 



KIND OF SARTU. 


Maximum temperature of 
the superior layer, the 
mean temperature of the 
ambient air being 77® F. 




Moist earth. 


Dry earth. 


Silicious sand, yellowish smiv . - 


o 

99-05 
9910 
99-28 
96-13 
103-55 
99-50 


o 
112-65 


Ciilcarpoiis mtiq. whitii^h imiv ............. 


112-10 


Ara^illacoous earth, vellowish' gray 

Oatcarcous earth, w^ite 1 

Mould, blackish prav 

Garden earth, blackish crav 


112-32 
109-40 
117-27 
113-45 







The differences of temperature exhibited by the two col- 
umns are due to the heat expended in the evaporation of a 
lH)rtion of the water in the moist earth, while the differences 
botwoon the substances are to be ascribed principally to the 
i*i>lors, though the textui*e may have some effect. 

Absi>rptive jH^wer is connected with that of emission ; and 
thoi>e boilios which i>ossess the greatest absorptive power for 
heat of a low intensity, also possess the greatest emissive 
power for heat of the siune kind. But the preceding re- 
marks have reference to the ravs from the sun and not to those 
of dark heat, and here I must stop to recall the fact which 
is frequently neglected, even by scientific men, namely, that 
color has no effect u|X)n the absorption or emission of rays 
of low intensity. For example, if we pass our hands over 
a sign-board on which dark letters upon a white ground are 
exposed to the sun we can readily jKjrceive with our eyes 
shut the difference of tem|)emture; but this would not be 
the case were the board exposed in the dark to the heat of 



-1859] WRITINGS OF JOSEPH HENRY. 193 

a stove of a temperature below redness. Furthermore if the 
same board were exposed to the clear sky and suffered to 
cool by its own radiation no difference of temperature would 
be observed in the different parts of its surface, except a 
very slight one, which might be due to the difference of 
the radiating power possessed by the substances of which 
the black and white paints are composed. On this subject 
Prof Bache, the Superintendent of the Coast Survey, has 
made a series of very interesting experiments. He found 
that canisters of tinned iron painted externally of different 
colors and filled with heated water, required the same time 
to cool through a given number of degrees. The facts in 
regard to this point may be generalized by saying that color 
has no influence whatever upon the emissive power of differ- 
ent bodies, but that its influence is confined to the reception 
of rays of high intensity, or those which approximate in 
quality to the luminiferous emanations. Hence a black or 
a white dress is equally cool in the night, though in the 
sunshine the darker one would absorb the greater amount 
of heat. 

Besides the color, the humidity of the soil has great influ- 
ence upon the temperature it acquires, a portion of the heat 
being expended in evaporating the water. We have seen 
the statement somewhere that the average temperature of 
whole districts in Great Britain has been elevated one de- 
gree by the system of drainage adopted in that country. 

In addition to the preceding causes, there are two others 
which affect the temperature of the soil, namely, conduction 
and capacity for heat. In a porous, badly conducting sub- 
stance the heat which may escape from the surface is not 
readily supplied from the interior, and hence such bodies 
are long in cooling. Again, different bodies contain very 
different amounts of heat at the same temperature, and hence 
one body may take a much longer time to cool down to the 
same temperature through the same number of degrees than 
another. That two different bodies of the same weight at 
the same temperature possess different amounts of heat may 
be shown by first heating say a pound of each in boiling 

18-2 



194 



WRITINGS OF JOSEPH HENRY. 



[1855- 



waier, and afterwards plunging them separately into equal 
amounts of cold water of say 32° F. It will be found that 
the heat which they severally impart to the water in the 
two cases will be very diflferent. 

The following table, also from Becquerel, gives the relative 
retention of heat by diflferent soils, (that of calcareous sand 
being one hundred,) and also the time of cooling of cubes of 
3'2256 inches (550 cubic centimeters) of the different earths. 

Table of retention of heat, by Becquerel. 



KIND OF EARTH. 


Capacity for heat, 
tnat of calcareous 
sand being 100. 


Time required by 83 
cubic ins. of earth 
to cool from 144®- 6 
to 70*>- 2, the tem- 
perature of the sur- 
rounding air being 
6P- 2. 


'Calcareous sand 

Silicious sand 

Arerillaceous earth 


1000 
96-6 
68-4 
61-8 
490 


hours, 
8-80 
8-27 
2-24 


Calcareous earth 


210 


Mould _ 


1-48 



. Effect of Cold, 

While the periodic temperature of a given place de- 
pends upon the position of the sun in its course, the abnor- 
mal hot and cold periods, or terms, as they have some- 
times been called, are due principally to winds from certain 
directions. The cold terms in this country generally begin 
in the northwest and advance southerly and easterly, and 
are accompanied with winds from the north and northwest. 
We do not however intend in this place to discuss these 
abnormal variations of temperature, but to consider the 
effect of cold on different bodies, including plants and ani- 
mals. We shall first consider its effects on a surface of water. 

Effect of cold on water. — When the surface of water is ex- 
posed to a low temperature, the upper stratum is cooled, 
becomes specifically heavier and sinks. A lower portion 
then comes to the surface which in its turn is cooled, be- 



-1859] WEITINQS OF JOSEPH HENRY. 195 

comes heavier^ and again gives place to another stratum, to 
pass through the same process. This continues till the col- 
umn of water originally included between the surface and 
the bottom is reduced to a temperature of about 39® F., at 
which point the fluid ceases to shrink, or in other words to 
become heavier, but on the contrary, expands with every 
diminution of heat until it becomes entirely solidified. After 
it has assumed a solid condition, it follows the law observed 
by other solids and shrinks with every subsequent fall (5f 
temperature. After the water of a given reservoir has arrived 
at a temperature of 39°, since it does not increase in weight, 
it continues to float on the surface, and is rapidly cooled down 
to 32°, or the point of congelation. Before however it can be 
converted into a solid at this temperature, it is necessary to 
abstract from it a large amount of .latent heat. 

To render this plain, let us suppose a lump of ice, taken 
at zero, and with the bulb of the thermometer in it, placed 
under such conditions that it shall receive from surrounding 
bodies one degree of heat in one minute of time. We shall 
find in thirty-two minutes the thermometer will come up to 
the freezing point; but here we shall observe that the mer- 
cury ceases to rise, although the supply of heat remains the 
same, and it will continue stationary during one hundred 
and forty minutes, or until all the ice is melted, after which 
it will again begin to rise, and continue its upward march 
until the water begins to boil, when a second stationary point 
will be reached. The heat which continued to flow into the 
ice during the stationar.y period, was necessary to convert it 
from a solid to a liquid state, and inasmuch as it does not 
affect the thermometer, it has been called latent or concealed 
heat. Water at 32° therefore contains 140° of heat more 
than ice at the same temperature. 

In the freezing of water, a reverse process takes place, and 
140° of heat have to be abstracted before the liquid is con- 
verted into asolid. Freezing is therefore comparatively a slow 
process, independently of the previous cooling down of the 
whole mass in the reservoir to 39°, and the upper film to 
32°. For example, if on the exposure of a stratum of water 



196 WRITINGS OP JOSEPH HENRY. [185S- 

at a temperature of 20° above freezing, to the air below 32^^ 
it requires twenty minutes to reduce it to the point of con- 
gelation, one hundred and forty minutes will be required to 
solidify it — or seven times as long. 

In melting the ice, the same amount of heat has to be ab« 
sorbed, so that a large extent of deep water becomes a r^u- 
lator of temperature, preserving the air immediately over it 
at near 32°, though the atmosphere in the vicinity during 
the winter may be far below zero ; conversely in the spring, 
though the temperature of the same latitude may be 60° or 
even 80°, that of the air immediately over the water will be 
near 32°. It is evident from these facts that the deeper the res- 
ervoir, the longer will be the continuance of low temperature 
required to freeze the surface, and the longer the time neces- 
sary for melting it again. These principles are illustrated 
in our great lakes. The greatest known depth of Lake Su- 
perior is 792 feet, and soundings of 300, 400, and even 600 
feet are not uncommon. In the coldest weather, the water 
over these deeper places is above 32°, and does not freeze, 
while over the shallow parts a coating of ice is formed, which 
gradually cooled by the slow diffusion of the water under- 
neath, retains its solidity until the last of June. Indeed, ice 
is sometimes found at the surface in the middle of July. At 
this period of the year, or a little later, the smaller ponds of 
water in the vicinity have a temperature of 72° to 74°. Lake 
Erie, being much shallower, sometimes freezes entirely across, 
and becomes in summer heated throughout its extent to 
nearly the temperature of the supernatant air. At the 
beginning of September, 1857, the temperature of Lake 
Huron was 56°, while that of the water from Lake Erie, 
which passed over the falls of Niagara, was 72°, precisely 
that of the air. 

All bodies, as we have previously said, in passing from a 
liquid to a solid state, tend to assume a regular geometrical 
arrangement called crystals. This is particularly observable 
when the process has been slow, and undisturbed by agita- 
tions and tremors. The form peculiar to each substance is 
exhibited when a portion only of liquid has assumed tlie 



-1859] WHITINGS OF JOSEPH HENRY. 197 

solid state, as in the case of the shooting of spicules across 
the surface of water in a metallic basin exposed to the cold. 
It will be found on inspection that the filaments of ice ar- 
range themselves at definite angles of either 60° or 120°, and 
that the triangular openings are bounded by sides making 
the same angles with each other. In reference to crystalli- 
zation, there is an important law to be borne in mind, 
namely, that the axis of the crystal always tends to be at 
right angles to the surface of the cooling mass. For exam- 
ple, if a quantity of melted zinc be poured into a cylindrical 
hole in cold sand, and the bar thus formed be broken across, 
the crystals will be found to be arranged in the form of radii, 
with their bases in the circumference; and in some cases 
there will be found a cylindrical hole along the axis, from 
which the metal has been drawn away by the shrinking at 
the time of cooling and crystallization. A precisely analo- 
gous arrangement takes place in the freezing of water, which 
may be observed by placing a quantity of this liquid in a 
globular glass vessel, and submitting it to a temperature of 
some 10° below freezing. We shall find then that the crys- 
tallization will begin at all sides of the globe, and proceed 
gradually towards the centre, expelling before it all the 
air, and most of the foreign substances which may be con- 
tained in the water. If the cold be continued, the freezing 
will proceed toward the middle, until finally the process 
would end by collecting at this point a quantity of air sur- 
prising in amount. Before this takes place however, the 
glass vessel will be broken by the expansion of the ice. The 
crystallization at the upper surface of the water will be some- 
what irr(^ular at first; the spicules of ice around the margin 
will tend to*shoot out at right angles to the surface of the 
glass ; but after a pellicle has formed over the top of the fluid, 
this will serve as a point of attachment, and the crystalliza- 
tion will go on, as in the other case, at right angles to the 
surface; the air bubbles will be driven down before it, and 
if the freezing be very gradual the air will be entirely ex- 
pelled, and the ice assume a perfectly transparent and hom- 
ogeneous structure. If the freezing be more rapid, the air 



198 WRITINGS OP JOSEPH HENRY. [1855- 

wbich has been expelled from the higher stratum will be 
caught by that next below., and in this way we shall have a 
series of air-bubbles extending downwards to the surface of 
the unfrozen water. 

Accustomed as we are to see bubbles of air rise in the 
water, it would appear at first sight that the bubbles seen in 
ice come up from the water below; but from actual observa- 
tion in the manner we have described, it is clearly proved 
that the bubbles are composed of. air which had been ab- 
sorbed at the surface of the water and expelled downward 
from stratum to stratum in the process of freezing. 

The ice then over a lake or pond consists of crystallized 
water, of which the axis of crystallization is at right angles 
to the surface and the principal cleavage in the same direc- 
tion. It results from this that in the thawing of the ice in 
spring it tends to resolve itself into innumerable prismatic 
crystals at right angles to the surface, and is liable to be dis- 
integrated by a strong wind in a single night, thus produc- 
ing the phenomena of a sudden disappearance of ice over a 
large surface, a fact which has been erroneously attributed 
to its sinking, an evident impossibility, since the minutest 
portion of crystallized water is specifically lighter than the 
same substance in a liquid form. General Totten several 
years ago arrived at the same conclusion as to the sudden 
disappearance of ice which I have demonstrated in the ex- 
periments before mentioned. 

Ice before it tends to give way becomes pervious to water, 
which is readily transmitted through the interstices of the 
crystals; hence those who are accustomed to travel on frozen 
lakes or rivers are aware of the fact that so long as the water 
of the melted snow does not pass through the surface of the 
ice underneath, it is safe and in a sound condition, though 
we must be careful not to confound this water with, that 
forced up by hydrostatic pressure from below, on account of 
the bending downwards of the whole field. 

A simple method has been proposed for determining the 
relative severity of different winters, by observing the thick- 
ness of ice. For this purpose a sliallow vessel of water is 



-1859] WRITINGS OF JOSEPH HENRY. 199 

exposed to the air and the thickness of the ice produced 
measured each dav. From what has been said it is evident 
— ^first^ that the vessel should be made of wood or some other 
non-conducting substance, in order that the freezing may not 
take place at the sides ; and second, that the water should be 
always of the same depth; for if there be two vessels of the 
same diameter, one containing more water than the other, the 
thickness of ice formed in the two will be different, unless the 
fluid in both is at the temperature of thirty-two degrees at the 
commencement of the exposure. If we would ascertain more 
accurately the measure of effect, the ice must be broken and 
its thickness measured or the amount weighed very carefully 
every day, for if we suffer it to accumulate we shall have a 
less result, since the first coat tends to screen the water, so 
that with the same temperature the process goes on more 
slowly. This method is very simple, and when properly 
employed furnishes reliable data for determining the relative 
intensity of different winters. By simply measuring the 
thickness on a lake or pond from year to year we may ap- 
proximately arrive at a similar result. But as we have said 
the upper stratum screens the lower ones, and a knowledge 
of this fact has been taken advantage of in some parts of 
New England to increase the quantity of the ice for econom- 
ical purposes. To this end water is suffered to flow over a 
surface of ice abeady frozen, and thus by frequently repeat- 
ing the operation a much greater aggregate thickness of ice 
is produced. Ice made in this way is more porous however 
and contains more air than that formed by ordinary freezing, 
since all the air evolved from the strata after the first must 
be retained by the next below. 

The more solid the ice, the longer it will resist thawing ; 
first, because it contains more water under a given external 
surface, and second, because a portion of radiant heat is 
always absorbed at any surface, whether it be external or 
internal ; for example, if we expose a piece of ice containing 
a bubble of air to a source of radiant heat, we shall find that 
the bubble will gradually enlarge, thus proving an inter- 
nal melting to be going on. In the preservation of ice for 



200 WRITINGS OF JOSEPH HENRY. [1855- 

domestic purposes it is therefore important that it should 
be gathered in masses as thick and large as possible. The 
lower side of the ice, as a general rule, contains more impuri- 
ties than the upper, since the process of crystallization tends 
to expel all the foreign ingredients downwards ; and hence 
a storehouse filled with thin ice will contain more impuri- 
ties, and, on account of the multitude of bubbles and amount 
of surface exposed, will melt much sooner than if well packed 
with thicker blocks. The temperature of ice moreover may 
be reduced considerably by exposure for some time to the 
weather, when below the freezing point, and thus the value 
of its cooling effect be enhanced. This diminution of tem- 
perature however is continued only by the slow conducting 
power of the ice, and though it may retard considerably the 
melting of the mass, we think the^eflfect is scarcely percep- 
tible in ice transmitted to warmer climates. We have never 
found a thermometer, inserted in a hole in the centre of 
blocks of Boston ice, in the city of Washington, to sink below 
32®. In filling the ice-house however and in compacting 
the mass, advantage should be taken of the coldest weather. 

In the preservation of ice the smaller the amount of sur- 
face exposed between the several parts, and the greater the 
amount accumulated in a given place, the longer it will resist 
melting ; for the tendency to become liquid will be in propor- 
tion to the surface exposed, since the heat which produces 
this effect must pass through the surface; for example, in a 
cubic block of ice, measuring one foot on each edge, there are 
six surfaces exposed, each one foot square. Now if we cut 
this same block into two parts, by a plane parallel to one of 
the sides, we shall present two additional faces each a square 
foot in extent, and the aggregate amount of surface exposed 
will be increased in the ratio of six to eight. For a similar 
reason, if we have two ice-houses of like form, the one ten and 
the other twenty feet in diameter, the capacity will be in 
the ratio of one to eight, while their surfaces will be as one to 
four ; hence the tendency to resist melting will be in direct 
proportion to the diameters of reservoirs of similar forms. 

Of all geometrical solids, a sphere is that which contains 



-1859] WRITINGS OP JOSEPH HENRY. 201 

the greatest amount of space in a given surface. All other 
conditions being equal, we should choose this form of ex- 
cavation for preserving ice ; but on account of the diflSculty 
of lining a pit of this shape, we may select the next most 
economical form, which is the cylindrical. It is scarcely 
necessary to mention in this connection the fact that, in 
order to succeed in preserving ice, it should be well pro- 
tected from the surrounding earth and air by strata of non- 
conducting materials, such as straw, powdered charcoal, or 
saw-dust, the greater the thickness of which, the better the 
purpose in view will be answered. The house should also 
(as an additional precaution) be shaded above by trees, and 
have the cover painted white, to reflect back the more intense 
rays which may reach it indirectly. Morever the ice should 
not be suffered to rest upon the bare ground below, but on 
double floors, between which a non-conducting substance 
is placed, communicating by holes with a deep pit or drain 
through which the water from the melted ice may percolate. 
We have stated that water at 39°1 begins to expand, and 
that this expansion increases until solidification takes place. 
The force exerted by this expansion is immensely great, 
being suflBcient to burst a cannon or to cause water to pass 
in the form of a fine 'frost through the pores of solid metal. 
When however this expansion is opposed by a sufficient ex- 
ternal pressure the water is not converted into a solid at 
thirt)'-two degrees, but assumes this condition at a lower 
temperature; a piece of ice therefore at thirty-two degrees 
subjected to a great pressure ought to be converted into a 
liquid; and this may serve to explain a fact frequently 
noticed, that pieces of ice thrown upon each other adhere at 
the points of contact — ^the percussion changing these surfaces 
from a solid to a liquid, which immediately afterwards solid- 
ifies again. But this cause is scarcely sufficient to explain 
the very remarkable fact that if two lumps of ice be placed so 
as to present two flat surfaces and these be pressed together 
they will unite as one mass; and this will take place even 
in hot water while the external surface is rapidly melting. 
The pressure necessary to bring them into contact would no 



202 WRITINGS OF JOSEPH HENRY. r^^^^- 

doubt tend to produce the effect we have already mentioned*, 
though it is not improbable that the melting of the ice, as in 
the case of the evaporation of water, tends to reduce the tem- 
perature slightly below 32°. Prof. Tyndall, of the Royal In- 
stitution, has recently made an interesting series of experi- 
ments on the plasticity of ice. He finds that it may be bent 
and moulded into a variety of forms by subjecting it to pres- 
sure, particularly when near the melting point, and has 
very ingeniously applied this property to the explanation of 
the stratified appearance of some of the glaciers. If pressure 
is applied to any plastic substance in which are disseminated 
globules of air or irregular patches of other material, the 
mass will assume a lamellar structure at right angles to the 
direction of the compressing force ; and in this way the 
laminated appearance which is exhibited after the conflu- 
ence of two separate streams of ice which exert a great 
pressure upon each other is explained. 

It is well known that when alcohol and water are mixed 
together the attraction of the two bodies is so great that a 
diminution of bulk and a consequent rise of temperature 
ensue. The same aflBnity exists between ice and alcohol; 
but when these are mixed, strange to say, a considerable 
diminuiion of temperature is the result; and those who 
habitually or otherwise mingle these two ingredients as a 
beverage, are sometimes surprised to find the fragments of 
ice frozen in a solid mass to the spoon by which the mixture 
is stirred. When two liquids having an attraction for each 
other are mingled together and a diminution of bulk ensues, 
heat must be evolved on account of the power generated by 
the approach of the atoms. For an analogous reason, when 
the attraction between the atoms of two bodies is diminished 
a quantity of heat must disappear; hence when a solid is 
dissolved in a liquid for which the attraction is not very in- 
tense, a quantity of heat disappears or cold is the result. In 
the case of the alcohol and ice, the cold produced by the 
liquefaction of the solid greatly exceeds the heat which might 
be produced by the union of the water and the alcohol. 
When the affinity however is very great, as between nitric 



-1859] WRITINGS OP JOSEPH HENRY. 203 

acid and copper, then the heat of the chemical combination 
of the two substances far exceeds the cold due to the lique- 
faction of the solid, and a high temperature in the mixture 
is the result. 

On the same general principle is explained the melting 
of ice by sprinkling the surface of it with salt, — a process 
sometimes resorted to for clearing the sidewalks after an in- 
tense cold has succeeded rain. The union of salt and ice pro- 
duces a liquid the freezing point* of which is many degrees 
below that of water; and hence on their contact in a solid 
state, liquefaction necessarily ensues; and this in accordance 
with the general law must be attended with a great reduction 
of temperature in the surrounding bodies; on which fact de- 
pends the application of salt and snow to artificial freezing, 
as in the manufacturing of ice-cream. In places where ice 
is scarce the same principle may be applied to produce a 
much greater reduction of temperature from a smaller quan- 
tity of this substance. Three parts of ice and one of salt 
mixed together in a thin vessel will reduce the temperature 
of a large quantity of water; and since the same salt may 
again be obtained in a solid form by exposing the solution 
to the sun we think such a freezer might in some cases be 
economically employed. 

The artificial production of ice in hot countries on a scale 
sufficient for domestic use, has of late it is said been success- 
fully accomplished. An attempt of this kind was made a few 
years ago at New Orleans, by means of the rapid evaporation 
of water, but the cold produced in this way baing small the 
process was not sufficiently economical to enable the manu- 
factured article to compete in price, in that city, with the 
abundant supply of ice imported from New England. 

Another process, which is said to be more effectual, is that 
of a Mr. Harrison, of England, and consists in the evapora- 
tion, liquefaction, and re-evaporation of ether. If the bulb 
of a thermometer covered with cotton and wet with ether bo 
exposed to the atmosphere, the cold produced by evapora- 
tion will cause the mercury to descend many degrees below 
the freezing point; and if the evaporation be made to take 



204 WRiriNQS OF JOSEPH HBNBY. [1355* 

place under the receiver of an air pump, a much greater re- 
duction of temperature will be produced. 

Although we have not seen any account of the apparatus 
for reducing to practice the plan above referred to, we can 
readily imagine an arrangement which would produce the 
result. For this purpose, it would be sufficient to put the 
water to be frozen in thin tightly closed vessels, and place 
them in a large receiver containing ether, the latter being 
connected with an air pump, of which the upward stroke 
should exhaust the atmosphere, and the downward stroke 
re-condense the vapor in a separate vessel, to be again let 
into the freezing receiver, and so on. 

The establishment of the ice trade, for which the present 
age is chiefly indebted to an enterprising citizen of Boston, 
must have a beneficial eflTect upon the sanitary condition of 
the world. The white man is especially adapted by his 
physical organization to the temperate regions, and succumbs 
to the intensity of the prolonged heat of the tropics unless 
through the agency of science he is enabled to ameliorate 
the eflfects of the ardent rays of a nearly vertical sun. An 
abundant supply of ice not only adds to the comfort of the 
European in India, but is indispensable to the continuance 
of his health. The use of this article will probably be very 
much extended, and by a suitable system of ventilation ap- 
plied to the cooling of the air of apartments in a manner 
analogous to that of heating them during the rigor of winter 
at the North. 

The expansion of a quantity of water passing into a solid 
state will be in the direction of least resistance, and hence 
we find a bulging up in the centre of the ice in a pitcher; 
but if the freezing be continued the thickening of the ice in 
this direction will produce a re-action in other directions, 
which causes the rupture of the vessel. This expansion, as 
we have stated before, only takes place while the water is in 
the act of solidifying; and it is not the stratum of ice first 
formed which causes the bulging up in this case, but the ex- 
pansion of the water beneath. This is fully explained by 
the plastic character of ice before mentioned. If the bulg- 



-1859] WRITINGS OF JOSEPH HENRY. 205 

• 

ing up however be too great, cracks are produced at the most 
elevated parts. 

After a quantity of water has been solidified it ceases to 
expand ; and with a still further diminution of temperature 
shrinks, in accordance with the law to which all solid bodies 
are subjected. Indeed it is now known that most liquid sub- 
stances which pass into the solid state enlarge their volume 
at the moment of transition, and that the phenomenon ex- 
hibited by ice is only a conspicuous illustration of a general 
rule. Ice once formed is found to'shrink more rapidly with 
a diminution of temperature than any other substance on 
which experiments have yet been made. 

The expansion of water and shrinking of ice serve to ex- 
plain a variety of phenomena presented in the operations of 
nature and the processes of the arts. Those who reside near 
the borders of rivers or fresh-water lakes are often startled 
during cold winter nights by explosions apparently as loud 
as those of discharges of heavy ordnance. These are pro- 
duced by the rupture of long lines of ice — the gradual shrink- 
ing of which has been going on during the reduction of tem- 
perature tending to bring the whole mass into a state of ten- 
sion, which is relieved by the sudden giving way along the 
line of least strength. I am informed by Captain M. C. Meigs, 
who has paid particular attention to the cracking of ice on 
Lake Champlain, that it most frequently takes phice in the 
narrower parts of the lake — the shrinking of portions on 
each side of this line of least resistance tends to separate the 
two masses. The water sometimes rises in the cracks thus 
formed, a new freezing takes place, and when the weather 
moderates and the field expands to its original dimensions, 
it becomes too large for the area it covers, and long ridges 
are thrown up. 

A similar effect is sometimes produced on the surface of 
damp ground subsequently frozen. During the winter of 
1856 and 1857, we received accounts of injury done to several 
brick houses by the separation due to the shrinking of the 
surface, passing through the foundation of the edifice, and 
extending up along the walls. We might infer from the 



206 WRITINGS OF JOSEPH HENRY. [1855- 

principles already stated that the line of separation would 
in preference pass through a house, as this is the direction of 
least resistance, for the cellar may be considered as a line of 
fissure between the two masses of earth, or a crack already 
commenced. 

During a very cold night when the temperature is rapidly 
diminishing, and the ground covered with snow slightly 
encrusted on the surface by previous thawing and freezing, 
a continued series of minute explosions may be heard de- 
pending in frequency and loudness upon the thickness or 
thinness of the crust. In some cases it resembles a crack- 
ling, and at others a series of distant though not loud or 
sharp explosions. 

There is a phenomenon connected with ice in rivers 
which has given rise to much discussion as to its cause. I 
allude to the freezing which takes place at the bottom of run- 
ning streams, where in some cases the ice remains until it is 
separated by its buoyancy and rises to the surface. It pre- 
sents a peculiar angular appearance, and is sometimes known 
by the name of anchor ice. Its formation appears to be an 
exception to the general rule of the freezing of water, which 
on account of the decreasing density usually takes place at 
the surface. It was at first supposed that it was due to the 
radiation of heat through the clear water above ; but Arago 
has shown that this explanation cannot be the true one, 
since rays of low temperature cannot pass through water, 
and hence no such radiation can take place. A more prob- 
able explanation has been given, I think, by the same 
author, in referring it to the fact that still water can be re- 
duced below the freezing point without congealing, and that 
it will immediately be converted into ice if a bit of solid 
matter be thrown into the vessel in which the experiment is 
made, which may serve as a nucleus for the crystallization. 
When water in this state is passing through a rapid channel 
it is mixed together and the coldest as well as the warmest 
part is brought into contact with the bed of the stream, the 
materials of which acting as a point of rest serve as a basis 
of crystallization. 



-1859} WRITINGS OF JOSEPH HENRY. 207 

Peculiar mechanical efifects are sometimes produced by 
alternations of thawing and freezing, — as for example in 
the case of water pipes constructed of lead or other malleable 
metal. To render this plain let us suppose a lead pipe one 
foot in length to be filled with water, and after being her- 
metically sealed at each end exposed to a low temperature; 
the expansion would merely stretch the pipe, the extension 
not being sufficient to burst it, and no continuation of cold 
or increase of its intensity would produce any further effect, 
as this would merely cause the ice to shrink; neither would 
thawing and re-freezing produce any effect, since the water 
Would merely return to its original volume, and the ice again 
expand to the same extent as before; but if the pipe com- 
nmnicated with a reservoir of water, so that when the thaw- 
ing took place, the whole space, enlarged by the previous 
freezing, were again filled with water, a second freezing would 
produce another enlargement of its internal capacity, and a 
third thawing and freezing, under the same circumstances, 
would repeat the process until at length the sides of the tube 
would give way. 

Effect of cold on plants. — Plants filled with sap and exposed 
to a low temperature are variously affected, according to the 
character of the plant, the duration of cold, and the season 
of the year at which it occurs. A sudden cold will tend to 
burst the cells. The velocity of the motion of the sap de- 
pends principally on the amount of evaporation from the 
leaves and stems, and this diminishes with temperature, all 
other things being the same; hence there is a certain degree 
of cold at which the sap ceases to flow, and the functions 
of the plant are suspended. 

The different parts of the same plant are killed at differ- 
ent temperatures below 32°; the more succulent and tender 
growths suffer first, and the woody portion, or that in which 
the sap is better defended by non-conducting materials, last. 
A sudden fall of temperature, (even though it be extreme,) if 
of short duration, may not penetrate to the sap and produce 
freezing. It would also appear that the sap of different plants 
congeals at different temperatures, and it is highly probable 



208 



WRITINGS OF JOSEPH HENRY. [1855- 



that other changes than those of a mechanical character are 
produced ; but on this subject much research is required, and 
every intelligent fiarmer may add important materials to our 
stock of knowledge by carefully recording the observations 
he may make relative to the reduction of temperature, and 
its continuance, by which certain plants are destroyed. 

It is shown by repeated observations that alternations of 
freezing and thawing are more hurtful to the tender plant 
than a uniform continuation of cold ; whether this is pro- 
duced by an action analogous to that we have described in 
reference to the water-pipe, or is due in part to other changes 
we are unable to say. When however the sap of a plant 
killed by frost is examined with a microscope, we find in it 
portions of destroyed tissue. It has also been observed 
that air may sink a few degrees below the freezing point 
without injury to the plant, provided the air at the time 
be very dry. It would seem from tliis that the freezing of 
the vapor and the production of the minute crystals which 
constitute hoar frost are in a degree essential to th.e effect. 

As a general deduction from chemical and mechanical 
principles, we think no change of temperature is ever pro- 
duced in plants without the concurrence of actions such 
as here indicated. Hence, in mid-winter, when all vege- 
table functions are dormant we do not believe that any heat 
is developed by a tree, or that its interior differs in tem- 
perature from its exterior further than it is protected from 
the external air. The experiments which have been made 
on this point, we think, have been directed by a false anal- 
ogy. During the active circulation of the sap and the pro- 
duction of new tissue, variations of temperature belonging 
exclusively to the plant may be observed ; but it is incon- 
sistent with general principles that heat should be generated 
where no change is taking place. 

Effect of cold on animals. — All animals, so long as life con- 
tinues, generate heat, and have temperatures peculiar to 
themselves. In the higher class of aiij-breathing animals 
this temperature varies within comparatively slight limits 
under the influence of motion, rest, or of external circum- 



-1859] WRITINGS OF JOSEPH UENRY. 209 

stances; and a reduction of temperature by the application 
of external cold produces, as is well known, a sluggish con- 
dition, which finally terminates in death. The effect of 
external cold can be prevented by artificial covering, or it 
may be obviated, in the case of domestic animals, by an 
extra allowance of food. The sagacious farmer is aware of 
the fact that a well-sheltered enclosure for cattle is not only 
a humane but an economical provision. 

Many observations have been made on the temperature 
peculiar to diflTerent animals, and a considerable number of 
observations recorded of a less scientific character in regard 
to th,e eflFect of the variations of temperature to which they 
may be subjected without permanent injury. The most 
astonishing fact, and one which could scarcely bo believed 
if we were not in this country familar with it, is that many 
cold-blooded animals can be actually frozen, and be to all 
appearance dead, and yet be revivified by gradually thawing 
in water near the freezing point. 

Fish, as we are assured on credible authority, are often 
brought to our northern markets from a great distance in a 
frozen condition, and may be restored to life by the process 
we have mentioned. 

This is a subject, as it appears to me, of high interest in 
a physiological point of view, and would richly repay the 
application of well-devised systems of investigation. Can it 
be possible that the animal is frozen entirely through, and 
that every vital act is suspended ? To what degree can a 
like result bo produced on warm-blooded animals, and how 
far can the state of hibernation be prolonged without death 
to the individual? Will it ever bo possible, in the case of 
any of the higher mammalia to so maintain the unstable 
equilibrium of constitution as to prevent decay, and at tlie 
same time to preserve in a latent state the vivifying prin- 
ciple? Though investigations on this point would bo inter- 
esting we can scarcely hope to realize from them one of tlie 
fancies of Dr. Franklin, that of sending representatives of 
one age down to another to keep alive more actively the 
sympathies of the present with tlie past. 

14-2 



210 W&ITLSGS OF J06EPH HENRY. [1855- 

J^ed of cold an the ground, — ^Tbe depth to which ground 
is frozen in some places from year to year, is also an indica- 
tion of the severity of the seasons ; the effect of cold will 
penetrate very differently however in dry and moist soil; 
in the first it will depend aitirely on the conducting power 
of the material, and in the second, it will also depend upon 
the amount of water to be congealed. The conducting capac- 
ity being the same, the depth to which the given degree of 
cold will penetrate will be much greater in dry than in wet 
soil, on account of the great amount of latent heat given off 
by the water before it is solidified. In dry conducting.soil 
the propagation of cold downwards may continue some time 
after the surface of the ground has become considerably 
heated. 

In a conducting body all parts tend to an equilibrium of 
temperature. If the upper end of a vertical iron bar be 
heated and then removed from the source of heat, it gradu- 
ally becomes cooled, while the other parts increase in tem- 
perature, until gradually an equilibrium is established ; con- 
versely, if we cool the upper end of the bar, it will take heat 
from the next lower part ; and this from the next, and so on, 
until the cooling reaches the extreme end, which will be 
cooled last If, before the cooling has reached the lower end, 
we heat the upper part, the next below will be heated, and 
so on, proceeding downwards; thus waves, as it were, of 
heat and cold may be sent through the length of the bar, 
becoming less and less in intensity as they descend. In this 
way explanations have been given of the phenomenon of 
caverns colder in summer and warmer in winter, — ^the cold 
wave due to a lower temperature requiring six months to 
reach the point of observation. 

The freezing of the ground in certain soils is hurtful to 
vegetation ; the frozen stratum expanding irregularly from 
below heaves up the surface, and frequently loosens or breaks 
the roots of the plant. A covering of snow is a protection, 
since this substance from its flocculent nature and the air 
entangled in it is a bad conductor of heat. As a general 
rule during cold weather a thermometer in air on the snow 



-1859] WRITINGS OF JOSEPU HENRY. 211 

will exhibit a lower temperature than one under the same 
material at the surface of the ground. This efifect however 
is not entirely due to the screening.influence of the covering, 
but in part to the fact that the intense rays of the heat of 
the sun as well as those of the light of the same body penetrate 
the crystals of the snow as they do the glass covering of a 
hot-house, and being absorbed by the dark ground beneath 
elevate the temperature. For the same reason in bright 
days the snow next to the slate roof of a house is seen to 
melt, while the upper surface remains unafifected. 

There is a singular phenomenon observed during the 
spring of the year in damp, sandy places, which has attracted 
much attention, namely, the ice-columns which spring from 
the earth during cold nights, elevating small gravel-stones 
on their tops, and raising as it were above its usual level the 
general surface of the ground. These crystals have been 
carefully studied by Professor John Le Conte, and appear to 
be due to the law we have before mentioned of the axis of 
crystallization being always at right angles to the surface of 
cooling, as well as to the attraction of the water for itself and 
the consequent excluding effect of all extraneous bodies. 
The water of which these crystals are formed is drawn up 
from below by capillarity ; is frozen as it comes up to the 
surface in vertical prismatic crystals ; a new portion is drawn 
between the basis of the crystals first formed and the ground, 
which is also frozen ; and so the process is continued until 
stopped by the failure of moisture, or the increase of the 
temperature due to the advancing heat of the day. 

The next subject in order of which we intended to treat 
is that of the vapor of water in the atmosphere ; but this is 
of so important a character in its connection with all the 
phenomena of the fitful changes of the weather, and the 
peculiarity of climate, as well as with the agricultural prod- 
ucts of a country, that justice cannot be done to it within 
the limits assigned to meteorology in this Report, and there- 
fore we shall defer it until next year. * 

♦ [Forty-three pages of Meteorological Tables following this part are 
omitted in the piesent re-print.] 



212 WRITINGS OF JOSEPH HENRY. [1855- 



METEOROLOGY IN ITS CONNECTION WITH AGRICULTURE. 

PART IV. — ATMOSPHERIC VAPOR AND CURRENTS. 
(Agricultural Report of Commissioner of Patents, for 1858, pp. 429-498.) 

In the preceding articles on Meteorology, it has been shown 
that the great motive power which gives rise to the various 
currents of the aerral covering of our globe is the unequal 
distribution of the heat of the sun ; the elevated temperature 
of the equatorial regions heating the air causes it to ascend 
and flow over toward the pole, while the cold of the frigid 
zone produces a condensation of the air, which gives rise to 
downward currents in that region, and a spreading out there 
in all directions towards the equator. 

The simplicity of this movement is first interfered with by 
the motion of the earth upon its axis, which gives to all the 
currents flowing toward the equator a curvature to the west, 
and to all those flowing from the equator a curvature to the 
east. Another perturbing influence is the unequal heating 
of the several parts of the different zones of the earth, con- 
sisting as they do of alternations of land and water. But the 
great perturbing cause is the var3ung quantity of moisture 
which exists rn the atmosphere, and which by its increase 
and diminution gives rise to the varying conditions of the 
weather, and produces the fitful and almost infinite variety 
of meteorological changes which occur at different times and 
in different places. 

The present essay will be principally devoted to an expo- 
sition of the phenomena of the vapor of the atmosphere, in- 
cluding that of the various aqueous meteors, such as rain, 
hail, hurricanes, tornadoes, &c. Tlie meteorology of North 
America, as well as its geology, is exhibited on a large scale, 
and affords one of the best fields on the surface of the globe 
for studying the general movements of the atmosphere. The 
subject has received much attention on this side of the At- 
lantic, and a number of laborers have dcvot<3d themselves to 
it with ardor and success ; but we regret that the discussions 



-1859] WRITINGS OP JOSEPH HENRY. 213 

which unavoidably arise among diflForent investigators, have 
not always been carried on with the calmness and modera- 
tion with which the pursuit of truth should always be con- 
ducted. Indeed, meteorology has ever been a source of con- 
tention, as if the violent commotions of the atmosphere 
induced a sympathetic effect in the minds of those who have 
attempted to study them. 

We have stated in the previous articles that we have no 
hypotheses of our own to advocate ; and while we attempt 
to reduce the multiplicity of facts which have been collected 
in regard to this subject to general principles, we shall aim 
at nothing but truth, and endeavor to select from the various 
hypotheses which have been proposed, such as in our judg- 
ment are well founded on the established laws of force and 
motion, and which give the most faithful and explicit ex- 
pression of the phenomena. We shall be ready at any time 
to modify or change our views as soon as facts are discovered 
with which they are incompatible, and indeed we shall hold 
most of them as provisional truths which may serve to guide 
our inquiries and which are to be established, modified, or 
rejected by the results of subsequent induction. While the 
general principles of meteorology are well understood, the 
facts relating to it on account of the variations and multi- 
plicity of condition are the most complex of those of any 
branch of physical science. It has been properly said that 
astronomy is the most perfect of all branches of knowledge 
because its elements are the most simple; and we may say, 
for a like reason, that meteorology is the least advanced be- 
cause its phenomena depend upon the concurrence of so 
many and so varied causes. 

Vapor of tlie Atmosphere. 

The air at all times contains water in an elastic, invisible 
state, called vapor. To prove this it is sufficient to pour a 
quantitv of cold water into a bright metallic or glass tumbler, 
the outside of w^hich will become covered with dew. If the 
vessel were pervious to the liquid we miglit Suppose the water 
which appears on the outside to come from within, but this 



214 WRITiyOS OP JOSEPH HENRY. [18SS- 

cannot be the case with a metallic or gloss vessel, and the 
only source to which we can refer the dew is the atmosphere. 
The stratum of air immediately around the vessel is cooled 
by contact with its sides and a portion of its vapor reduced 
to water. The air thus cooled becomes heavier, sinks down 
along the side of the tumbler, and gives place to a new por- 
tion of which the vapor is also condensed; and in this way 
the process is continued as lon^ as the temperature of the 
water is below that of the surrounding air. If the water 
which trickles down the side of the vessel is chemically 
examined, it will be found in some cases almost entirely 
pure, and in others contaminated by animal and other 
effluvia which are diffused in the atmosphere. If the ex- 
periment be made on different days and at different seasons 
we shall find a greater or less reduction of the temperature 
of the liquid within the tumbler is required in order to 
produce a deposition of the vapor. The greater the number 
of degrees of this reduction of temperature the greater will 
be the evaporation from a given surface of water, and the 
more intense will be the different effects which depend on 
the relative dryness of the air. If the experiment be made 
in summer we shall frequently find but a small reduction 
of temperature necessary to produce the deposition of moist- 
ure on the outside of the tumbler, and if we attend to the 
state of our feelings at the same time we experience that 
peculiar sensation which is referred to what is called the 
closeness or sultriness of the atmosphere, and which is caused 
by the large amount of vapor with which it is charged. 

TJie phenomena of vapor by itself in a vacuum, — To under- 
stand even approximately the effects due to the vapor in the 
atmosphere it is necessary that we should first carefully study 
the phenomena of water in an aeriform condition as it exists 
by itself or separated from the atmosphere; and for this 
purpose we may employ the ingenious method devised by 
Dr. Dalton, of Manchester, England, to whose researches in 
meteorology and other branches of physical science we are 
more indebted than to those of almost any other individual 
of the present century. He employed in these researches a 



-1859] WRITINGS OF JOSEPH HENRY. 215 

glass tube of about 40 inches iu length, closed at one end, 
and filled with dry and warm mercury. The tube thus 
filled was inverted with its lower end in a basin of the same 
metal, and thus formed an arrangement similar to that of 
an ordinary barometer, in which the pressure of the air, as 
is well known, forces up the mercury and keeps it suspended 
at an elevation of 30 inches, when the experiment is made 
at the level of the sea. The space above the mercury is a 
Torricellian vacuum ; that is, a space void of all gross 
matter, save a very attenuated vapor of mercury, which can 
also be removed by a reduction of temperature below the 
50th degree of Fahrenheit's scale, but the correction on this 
account is so small that it may be neglected. Into this 
vacuum Dr. Dalton. introduced a very small quantity of 
water, by forcing it from a small syringe into the mercury 
at the base of the column, whence it rose to the surface and 
was attended with an immediate depression of the mercurial 
column, which, when the temperature of the room was at 
60°, amounted to nearly half an inch. By this experiment 
it was proved that water at the ordinary temperature, when 
the pressure of the air is removed, immediately flashes into 
steam or vapor, and that the atoms of this vapor repel each 
other, thus producing an elastic force which depresses the 
column of mercury. In this experiment, the quantity of 
water introduced was but a few grains, yet it did not all flash 
into vapor, but a portion of it remained in the form of a 
thin stratum of liquid on the surface of the mercury. Its 
weight, however, was insufficient to produce the observed 
descent of the column, and its effect in this respect could 
readily be calculated, since its weight was known. The 
descent of the mercury was therefore due to the repulsion of 
the atoms of vapor, and the former afforded an accurate 
measure of the comparative amount of this force. 

The tube, as we have stated, was 40 inches long ; and since 
the column of mercury at first occupied but 30 inches of its 
length, the extent of the vacuum before the introduction of 
the water was 10 inches, and afterward lOJ inches. That 
the depression of the mercury is an exact measure of the 



216 



WRITIN09 OF JOSEPH HEUBT. 



[18S». 



elastic force or repulsion of the atoms of the aqueoas vapor 
will bo evident when we consider that if we remove the vapor 
the column will rise to 30 inches, and will then be exactly 
in equilibrium with the pressure of the external atmosphere, 
the two being in exact balance; but if after the lotFoduction 
of the vapor the column is reduced half an inch in height, 
it is plain that the force which produces this effect must be 
just equal to the weight of this amount of mercury. 

Dr. Dalton next diminished the length of this vacuum by 
plunging the lower end of the tube deeper into the basin of 
mercury, and thereby causing the upper end of the column 
to be projected farther into the tube; but this produced no 
difference in the height of the column, the top of which was 
still depressed to half an inch below the normal height of 30 
inches. From this experiment wo infer that the repulsion 
of the atoms of vapor cannot, like that of the atoms of air, be 
increased by external pressure; for when we attempt to 
coerce them into a smaller space by ex- 
ternal pressure, a portion of them is con- 
verted into water, and the atoms which 
remain in the aeriform condition exert 
the same amount of pressure as before. 

Dr. Dalton next increased the tempe- 
rature by surrounding the tube contain- 
ing the mercurial column with a latter 
tube filled in succession with water of 
different temperatures; this produced for 
each temperature a difference in the 
depression of the height of the column ; 
and when the water was at the tempera- 
ture of lOD" the depression instead of 
being half an inch was almost precisely 
three times as much. 

Fig. 1 represents the apparatus em- 
ployed by Dr. Dalton, in which a is the 
barometer tube filled with mercury to 
the height of/, and its lower end plunged 
into the basin of mercury c. The grad- 




-1859] 



WRITINGS OP JOSEPH HENRY. 



217 



uated scale for measuring the height of the column is 
denoted by b. The larger tube around the barometer tube 
to contain the water of different temperatures is denoted 
by d. A thermometer e is inserted at its upper end by 
which to ascertain the temperature of the enclosed water 
and, consequently, that of the vapor within the barometer. 

With this simple contrivance Dr. Dalton made a series of 
experiments to determine the repulsion of the atoms of 
steam; or in other words, the elastic force of aqueous vapor, 
corresponding to the different degrees of Fahrenheit's scale 
from zero up to the boiling point. To facilitate the opera- 
tions and to allow for any changes that might take place 
in the pressure of the atmosphere during the continuance 
of the experiment, another tube was placed beside the first 
in the same basin, and the descent of the mercurial column 
of the first tube estimated from the top of that in the second, 
which to render the measure more accurate may be effected 
by means of a small telescope, sliding on a graduated rod, 
and movable in a horizontal plane. 

By placing water of a given temperature within the outer 
tube and gradually cooling it after each observation, and . 
finally filling the same tube with freezing mixtures, a table 
similar to the following was constructed. Dalton's experi- 
ments however have b^en repeated with additional precau- 
tions by other scientists, and particularly by M. Regnault, 
from whose work the annexed table has been compiled. 

A — EUistic force of aqueous vapor ^ in English inches of mercury. 



^. 


0». 


P. 


2°. 


8«. 


4*>. 


5°. 


6<>. 


7<>. 


' 8°. 


9°. 


o 


Ins, 


Ins. 


Ins, 


Ins. 


his. 


Ins, 


Ins. 


Ins. 


Ins. 


Ins. 





0043 


0-046 


0-048 


0060 


0062 


0-055 


0-057 


0060 


0-062 


0065 


10 


0068 


0072 


0-076 


0078 


0082 


0086 


0090 


0094 


0098- 


0103 


20 


0108 


0118 


0118 


0128 


0129 


0-135 


0-141 


0-147 


0153 


0160 


80 


0167 


0-174 


0-181 


0188 


0196 


0-204 


0-212 


0-220 


0-229 


0-238 


40 


0-248 


0-267 


0-267 


0-277 


0-288 


0-299 


0-311 


0-323 


335 


0-348 


60 


0-361 


0-874 


0-388 


0-403 


0-418 


0-433 


0-449 


0-460 


0-482 


0-500 


60 


0618 


0-687 


0-656 


0-676 


0-596 


0-017 


0-639 


0-662 


0-685 


0-708 


70 


0-788 


0-768 


0-784 


0-811 


0-839 


0-868 


0-897 


0-927 


0-958 


0-990 


80 


1-028 


1-057 


1092 


1128 


1165 


1-203 


1-242 


1-282 


1-323 


1 •3(>6 


90 


1-410 


1-466 


1-601 


1-548 


1-597 


1-047 


1-698 


1-751 


1-805 


1-861 


100 


1-918 


1-977 


2-087 


2099 


2162 


2-227 


2-293 


2-361 


2-430 


2-501 



218 WRITINGS OF JOSEPH HBNRY. [1855- 

The first column of the above table gives the temperature 
of the water and vapor in the Torricellian vacuum for every 
ten degrees; the second, the depression of the mercury, or 
the elastic force of the vapor, corresponding to the several 
degrees of temperature of the first column. The remaining 
columns give the depression of the. mercury for the inter- 
mediate degrees, this arrangement being adopted to save 
space. 

For example, if we wish to know the elastic pressure of 
vapor at the temperature of 70°; by looking opposite to 70°, 
in the second column, we find 0*733 or nearly seven-tenths 
and a third inches of mercury. Again, if we wish the amount 
of repulsive force of the atoms of vapor at the temperature 
of 86°, we cast our eye along the line of 80° until it comes 
under the 6°, which is at the top of the table, and find 1*242 
or very nearly an inch and a quarter as the height of a 
column of mercury which vapor of water will balance with- 
out being condensed into a liquid at the temperature of 86°. 

By looking along the foregoing table it will be seen that 
equal increments of heat are attended with more than equal 
. increments of elastic pressure. Thus while the elastic force 
of vapor at 20° is sufiicient to depress the mercurial column a 
little more than one-tenth of an inch, at 40° it depresses it 
nearly two and a half times as much, at 60° five times, at 80° 
ten times, and at 100° nineteen times. The reason of this is 
not difiicult to understand, since it is evident that the elastic 
pressure of the vapor must be increased by the action of two 
causes: First, by increasing the temperature the vapor tends 
to expand just as air would do under the same circumstances ; 
and second, by the same increase of temperature a new por- 
tion of water is converted into vapor, which being forced 
into the same space, increases the density, and consequently 
the elasticity of the vapor which existed there before. 

Dalton also showed that there is a remarkable dif- 
ference between vapor which exists over water and vapor 
separated from the liquid from which it is produced. In 
the first case, as we have seen, every increase of temperature 
causes the formation of a new quantity of vapor which 



-1859] 



WRITINGS OF JOSEPH HENRY. 



219 



BBTvea to increase the density, and consequently the repulsive 
energy of the vapor previously existing. Hence, as we have 
shown before, the expansive power of vapor or steam in- 
creases in a geometrical ratio, while the temperature in- 
creases in an arithmetrical ratio, that is, an addition of a few 
d^ees of heat produces more than a proportional degree 
of elastic force. The case however is very different with 
vapor separated from the water from which it is produced; 
it then obeys the same law as atmospheric air and increases 
in elasticity with equal additions of temperature. 

It has been stated in a previous article that the atmos- 
phere increases its elastic force by one four hundred and 
ninetieth part for every degree of Fahrenheit above the 
freezing point; the vapor of water follows the same law. 
These facts are readily proved by the apparatus exhibited 

^ in Fig. 2. So long as any water e remains 

I '^feL^ above the mercury in the tube a, the latter 
^^ may be drawn up or pushed down into the 
reservoir without altering the height of the 
column of mercury c e. The higher the tube 
is drawn up, the more water will spring into 
vapor, while the tension or repulsive energy 
remains the same, as shown by the invariable 
height of the mercurial column. When the 
barometer tube is pushed down into the basin 
and the space above diminished, a portion 
of the vapor is converted into water, and this 
portion increases as the space is made to 
diminish. If however we draw up tlio tube 
so that all the water will pass into vapor, a 
further elevation of the tube will produce 
an elevation of the height of the mercurial 
column; tlie vapor will become rarificd and 
its elastic pressure will consequently be 
diminished, and hence the increased length 
of the column of mercury. If sufficient cold 
Pio. 2. and pressure could be applied to atmos- 

pheric air, it is not improbable that a portion might be con- 



220 WRmxQs OP Joseph henry. [ibss- 

verted into a liquid, just in the same way that an increase 
of pressure converts the vapor which fills the top of the 
barometer tube into water. This supposition is the more 
probable since several gases which were at one time consid- 
ered permanently elastic have been reduced in this way to a 
liquid by the application of a powerful pressure, combined 
in some cases with a reduction of temperature. 

The forgoing table is limited to 100®, and is sufficient for 
resolving problems relative to the hygrometrical condition 
of the atmosphere. It is however important for the use of 
the steam engineer that it should be extended to a much 
higher degree, and accordingly experiments have been made 
for this purpose by a number of persons, and particularly by 
M. Regnault, at the expense of the French government. 
From the table thus extended we may see that at the tem- 
perature of 212° the elastic force of vapor balances 30 inches 
of mercury, and is then just equal to the pressure of the 
atmosphere. This fact gives the explanation of the phenom- 
enon of boiling, since the vapor formed at the temperature 
of 212° has just sufficient repulsive power to expand beneath 
the pressure of the atmosphere, and to pass up in volumes 
through the water, giving it the peculiar agitation known 
as boiling. 

It is further evident from the same table that vapor is given 
oflf from ice even at zero, or 32° below the freezing point. 
If a lump of this substance on a cold day be placed under 
the receiver of an air pump, even when the apparatus is 
cooled down to zero, a portion of it will immediately spring 
into vapor, sufficient to fill the whole capacity of the cylinder 
when the air is withdrawn; and if this vapor in its turn be 
removed by working the pump another portion of the ice 
will pass into the state of vapor, and if the pressure of this 
be removed another quantity of ice will be evaporated; and 
if the pumping be continued sufficiently long all the ice will 
be dissipated in vapor without passing through the inter- 
mediate condition of water. Instead of continuing to work 
the pump in order to evaporate the ice we may produce the 
same eftect by placing within the receiver a broad dish con- 



-1859] WRITINGS OF JOSEPH IIKNRY. 221 

taining sulphuric acid, which will absorb the vapor as fast 
as it is formed. 

We may convince oursejves immediately of the evapora- 
tion of ice by exposing a given weight of it during a cold 
day in the shade while the temperature is below freezing. 
It will be found sensibly, though slowly, to diminish in quan- 
tity. The same effect is exhibited in the process of drying 
clothes in cold weather, which though they may be stiffened 
by the frozen water with which they have been wetted, soon 
become dry and pliable by the evaporation of the ice. 

The apparatus of Dalton enables us to make the follow- 
ing experiment, which has an important bearing on some 
of the phenomena of meteorology. If, while the column of 
mercury is at the temperature, for example, of 60°, and a 
small quantity of water is resting on its upper end, the space 
above being filled with vapor due to this temperature, we 
place under the lower end of the tube beneath the surface 
of the mercury a small crystal of common salt, it will rise 
through the mercury by its specific levity, and be dissolved 
in part or whole by the stratum of water at the top. Now 
as soon as this solution begins to take place we shall see the 
column of mercury ascend; a portion of the vapor will be 
absorbed, and the tension of the remainder be diminished. 

In this case the attraction of the salt for the particles of 
water neutralizes a part of their repulsive force and thus 
diminishes the weight of mercury the vapor can support. 
For the same reason salt water boils at a temperature several 
degrees higher than 212°, though the vapor produced in 
this case has only the elastic force of that due to pure water. 
From the foregoing we conclude that the quantity of vapor 
from the surface of the ocean is less and has less tension and 
density than that from the surface of fresh-water lakes at 
the same temperature. 

The table which was furnished by Dalton, and has since 
been corrected by more refined experiments, is of great value 
in various branches of science. The very simplicity of tlie 
method employed is an evidence of scientific genius of the 
highest character, and is well calculated to excite our ad mi- 



222 



WHITINGS OF JOSEPH HENRY. 



[lass^ 



ration as well as to call forth our gratitude on account of 
the important truths which it reveals. Dalton, although 
a profound thinker, and thoroughly imbued with a love of 
science for its own sake, was eminently a practical man in 
the proper sense of the term. He had not only the sagacity 
to frame significant questions to be propounded to Nature, 
but also the ingenuity to devise simple means by which the 
answers to these questions would be given in terms the most 
precise and accurate. 

The weighi of vapoi\ — There are other important questions 
to be answered in regard to the same subject; and the first 
we shall consider is the relative weight of a given quantity 
of vapor in a space fully saturated at different temperatures. 
The general method of ascertaining the weight of a given 
quantity of an aeriform fluid consists in weighing a vessel 
of known capacity when exhausted, and again when it is 
filled with the air or vapor of which the weight, or in other 
words the density, is desired. The difference of weights of 
the vessel in the two conditions evidently gives 
the weight required. This may serve to give a 
general idea of the method of determining the 
weight of vapor; but it may be well to dwell a few 
moments on a more detailed account of one of the 
processes which has been actually adopted. This 
consists in employing an apparatus formed of a 
glass globe a (Fig. 3) screwed at / to the top of 
a barometer tube e. The capacity of the globe is 
previously ascertained by weighing it empty and 
afterwards filled with mercury. The difference of 
weight gives the weight of mercury sufficient to 
fill it, and from this it is easy to calculate its con- 
tents in cubic inches or parts of a cubic foot. Next, 
a small hollow bulb of glass g^ is formed by the 
blow-pipe, and filled with a known weight of water. 
For this purpose the capillary tube c (Fig. 4, in 
which the bulb g is represented much enlarged) 
Fig. 3. jg plunged beneath a surface of water 6, and the 
glass gradually heated by a spirit lamp d, by which the air 




-1859] WIUTINGS OF JOSEPH HENRY. 223 

is partially expelled. It is then suffered to cool, wlicn by 
the pressure of the atmosphere 
a quantity of water is forced up 
into the bulb. This is made to 
boil rapidly so as to expel alons; 
Ivith the escaping steam all the 
air. The capillary end of the 
bulb being again plunged be- 
low the surface of the water, 
and the lamp withdrawn, the ^^°- ^• 

pressure of the atmosphere will now entirely fill the bulb 
with the liquid. The point of the capillary tube is then 
closed by melting it in the flame of tjie blow-pipe, and 
the bulb thus filled with water is again weighed. If from 
this last weight we subtract the weight of the glass we 
shall have the weight of the contained water. This bulb 
with its known amount of water is next placed in the 
glass globe a, (Fig. 3,) the long tube screwed in its place, and 
the whole apparatus filled with dry mercury and inverted 
in a basin i of the same metal. The mercury of course by 
its weight will descend from the glass globe into the tube, 
and sink until it becomes in equilibrium with the weight of 
the atmosphere, which as we have said before, will be about 
the height of 30 inches. The inside of the globe will then 
be a Torricellian vacuum, and the water if released from the 
small bulb in which it is contained would immediately flash 
into vapor by the unbalanced repulsion of its atoms ; and 
we -can readily release them from their confinement by 
directing upon the bulb for an instant a beam of heat from 
the sun by a burning glass. By this means the bulb will 
be broken, (particularly if formed of dark glass,) the water 
will be set free, and will be converted in part at least into 
vapor. The whole apparatus is then heated by plunging it 
into a water bath of which the temperature is gradually 
raised, or by heating the room in which the experiment is 
made, until all the water is converted into vapor. By care- 
fully noting the temperature at which the liquid disappears, 
we have from the previous table the tension of the vapor at 



224 WUITINQS OF JOS£PH HEMBY. [1855- 

iliis point; and since the weight of the steam which fills the 
globe is equal to the weight of the water originally contained 
in the small bulb, we have the weight of the vapor, and 
knowing the number of cubic inches of the capacity of the 
globe, we can easily determine the weight of a cubic foot of 
vapor at the temperature at which the experiment was 
made. 

In this experiment care must always be taken to determine 
the exact temperature at which the water disappears; for if 
a portion of water remains in the liquid state we shall not 
have the true weight of the vapor; and we are assisted in 
determining this point by the fact that in gradually increas- 
ing the temperature of the apparatus we shall find that at 
the moment when all the water is evaporated the vapor will 
change its rate of expansion, and be governed by the same 
law as that of the expansion of dry air. 

After having determined the weight of a given quantity 
of vapor, for example a cubic foot, by direct experiment ac- 
cording to the method we have described, the weight of an 
equal quantity of vapor at other temperatures may be deter- 
mined by calculation. For example, the density of the vapor 
(as in the case of air) will bo in proportion to its elastic force 
or the pressure to which it is subjected, if the temperature 
remained the same; hence from the table of elastic force 
already given, we may calculate the corresponding weights of 
a foot of vapor. The numbers thus obtained however must 
be corrected for the diminution of weight on account of the 
expansion due to increasod tomi)erature. In this way table- 
B was constructed, in which the first column indicates the 
temperature of every ten degrees of Fahrenheit's scale; 
the second column gives the weight of vapor in Troy grains 
contained in a cubic foot of space; the remaining columns 
give the weight of vapor at intermediate degrees. 



-1859] 



WRITINGS OF JOSEPH HENRY. 



225 



B- 


— Weight of vapor in a cubic foot of 


saturated air^ 


ingrains Troy. 


Degs. 
F. 


oo 


lo 


2o 


8<» 


40 


5<» 


6° 


70 


8*» 


9*> 


o 


Gr'Tts, 


Gr'ns, 


Or'ns. 


Or'na. 


ar'ns. 


Or'ns. 


Ghr'ns. 


Or'ns. 


Or'ns. 


Gr's. 





0-54 


0-56 


0-59 


0-62 


0-64 


0-67 


0-70 


0-73 


0-77 


0-80 


10 


0-84 


0-87 


0-91 


0-95 


0-99 


104 


1-09 


1-13 


119 


1-24 


20 


1-29 


1-85 


1-41 


1-47 


1-54 


1-60 


1-67 


1-74 


1-81 


1-89 


80 


1-96 


204 


212 


2-20 


2-29 


2-37 


2-46 


2-56 


2-65 


2-75 


40 


2-86 


2-96 


307 


3-18 


3-30 


3-42 


3-55 


3-67 


3-81 


3-94 


60 


408 


4-23 


4-38 


4-53 


4-69 


4-80 


502 


5-20 


5-38 


5-56 


60 


6-75 


6-95 


6-15 


6-86 


6-57 


6-79 


7 02 


7-25 


7-49 


7-73 


70 


7-99 


8-25 


8-52 


8-79 


908 


9-37 


9-67 


9-97 


10-20 


10-61 


80 


10-94 


11-29 


11-64 


1200 


12-87 


12-75 


1814 


13-54 


13-95 


14 37 


90 


14-81 


15-25 


15-70 


1617 


16-65 


1714 


17-64 


18-16 


18-69 


10-23 


100 


19-79 


20-85 


20-98 


21-53 2214 


22-77 


23-41 


24-06 


24-74 


25-42 



This table we shall see is of great importance in practi- 
cal meteorology, as it enables us to ascertain the weight of 
the vapor in a given portion of the atmosphere at different 
temperatures. 

The latent heat of vapor, — There is another circumstance 
in regard to vapor which is of essential importance in un- 
derstanding the part which it plays in producing the diver- 
sified changes of the weather, namely, the great amount of 
heat which it contains at different temperatures. It is well 
known that the quantity of heat that a body contains is not 
actually measured by the thermometer or the temperature 
which it exhibits ; for example, if a cubic foot of air at 00° be 
expanded without receiving or losing heat its temperature 
will be much diminished, because the same amount of heat 
which was before contained in a given space is now dis- 
tributed through a larger space. If an ounce of steam from 
boiling water, which indicates a temperature of 212°, be 
condensed in water at 60°, it will give out to the latter 
enough heat to elevate six times the quantity of water to the 
boiling .temperature ; that is, six times as much water 
through 152°, or. the same amount of water 912°; or in 
other words after having given out more than 900° of heat 
in the act of being converted from a vapor to a liquid, it 
still retains a temperature of 212°. The heat which is thus 
evolved, and is not indicated by the thermometer, (as has 
been stated in our preceding article with reference to the 

15.2 



226 WRITINGS OF JOSEPH HENRY. [1855^ 

melting of ice,)* is called latent heat. In thus condensing 
a given quantity of vapor, from water at different tempera- 
tures in a given quantity of cold water and noting the 
elevation of temperature of the latter, it has been shown by 
Dalton and others that an ounce of vapor at all tem- 
peratures contains very nearly the same amount of heat, 
adding the latent and sensible heat together. 

This constancy of the amount of heat arises from the fact 
that as we increase the thermometric heat a new portion of 
vapor is forced into the same space, its density increases, and 
the amount of latent heat is diminished ; hence if the at- 
tenuated vapor from ice were received in a syringe and sud- 
denly condensed until its density became equal to that of 
boiling water, its temperature would be 212°. 

On account of the great amount of latent heat of vapor, 
heat must be absorbed from all surrounding bodies during 
the process of evaporation; and in all cases of the reverse 
process, that is of the conversion of vapor into water, an 
equal amount of heat must be given out. This absorption 
of heat by vapor at the place of its formation, and the evolu- 
tion of an equal amount at the place where it is condensed 
into water is one of the most eflBcient means of varying the 
temperature of different portions of the earth from that which 
they would naturally acquire under the regular periodical 
variation due to the changes of declination of the sun. 

In the evaporation of a cubic foot of water it is known 
from experiment that an amount of heat is absorbed equal 
to that evolved from the combustion of 20 pounds of dry 
pine wood, and consequently every cubic foot of rain water 
which falls from the clouds leaves in the air above an equal 
amount of extraneous heat, whicli tends to abnormally raise 
the temperature due to the elevation, and to produce power- 
ful upward currents above, and horizontal motions of the air 
below. We may also recall in this place the fact that water, 
in passing from the state of ice to that of a liquid absorbs 
140° of heat, which is again evolved in the act of freezing, 

*[Seccr?j/e, p. 19^] 



-1859] WRITINQS OF JOSEPH HENRY. 227 

and that this also is an eflScient means by which colder por- 
tions of the earth are mollified in temperature.. 

In the explanatibns we have thus far given we have spoken 
of the increase of the repulsion of the atoms of water by an 
increase of heat. By this we mean the increased tendency 
which they have to separate from each other with a force 
which resembles simple repulsion, but which, if we adopt 
the vibratory theory of heat, will be due to the increased 
intensity of the oscillation of the particles. We have also 
employed the usual term "latent heat" to express the heat 
which disappears when a solid is converted into a liquid, or 
a liquid into a vapor — though this, according to the new 
theory of heat, would be expressed by the quantity of vibra- 
tion or mechanical energy which is absorbed in the change 
of state of the body and which will re-appear when the re- 
verse process takes place. To illustrate this suppose an up- 
ward impulse be given to a ball suflScient to throw it upon 
a shelf. In this case we may consider the mechanical energy 
as having been expended in producing this effect, although 
it is ready again to make its appearance and to do work when 
the ball is suffered to fall again to the level whence it was 
projected. 

Vapor in air. — ^We Jire also indebted to Dr. Dalton for 
another important series of experiments which relate to the 
mingling of air and vapor. In the experiments before given 
the vapor was weighed, and its temperature and tension 
determined in a separate state and unmingled with the air. 
To ascertain the effect which would be produced on the ten- 
sion of vapor when suffered to be exerted in a space already 
occupied with air of different densities. Dr. Dalton employed 
the same niethod of experimenting previously described. 
A barometer tube was filled and inverted, as before, in a 
basin of mercury, a quantity of air was then admitted, which 
rising into the Torricellian vacuum, pressed by its elasticity 
on the surfaco of the mercury and caused it to descend a 
given number of divisions of the scale which were accu- 
rately noted; a small quantity of water was next admitted, 
which rising to the top of the mercurial column was after a 



228 



WRITINGS OF JOSEPH HENRY. 



[1855- 



few moments in part converted into vapor while the mer- 
cury was observed to be depressed. When the experiment 
was repeated with dififerent quantities of air above the mer- 
curial column and at different temperatures, produced by 
varying the heat of the water in the external tube, or which 
would amount to the same thing, by varying the tempera- 
ture of the room, the remarkable fact was discovered that 
the depression of the mercurial column due to the introduc- 
tion of the water was precisely the same at the same tem- 
perature as when the experiment was made with a vacuum ; 
for example, at the temperature of 60°, whatever might be 
the elasticity of the air within the tube, the introduction of 
the water always gave an additional depression of half an 
Jnch. From this result the important fact is deduced that 
the tension or elastic force of vapor in air is the same as that 
of vapor in a vacuum ; from which we might also infer that 
the quantity of vapor which can exist in a given space al- 
ready occupied with air is the same as that which can exist 
in a vacuum at the same temperature. But this fact may be 
directly proved by an independent experiment. 
For this purpose let the globe a, Fig. 3, be filled 
with air, while the small bulb placed within con- 
tains a known quantity of water, and let the 
globe thus filled be screwed to the top of the 
barometer tube. If the apparatus be now par- 
tially filled with mercury so as to leave the globe 
nearly filled with air and the whole inverted with 
its lower end in a basin of mercury, the mercury 
will descend along the scale and will come to rest 
at a certain division, which will indicate the elas- 
tic force of the air in the globe ; if next the stop- 
cock be shut and the small ball be broken by the 
heat from a burning glass the contained water 
will, in part at least, spring into vapor; and if we 
gradually heat the globe until all the water dis- 
appears and note the temperature at which this 
takes place, the globe at this moment will be 
filled with air at a known density and with in- 




Fia. 3. 



-1859] WRITINGS OP JOSEPH HENRY. 229 

visible vapor of a known weight and temperature. If we 
calculate from the table B, (p. 225,) the amount of vapor which 
at this temperature existed in this globe while its interior 
was a vacuum, we shall find it precisely the same as the 
weight of that which the globe now contains when filled 
with air. If, for example, the globe be a foot in capacity 
and the small bulb contain 9*37 grains of water, the tempe- 
rature at which the water disappears being 75°, by pass- 
ing our eye horizontally along the table we shall find 
under 75° the same number of grains. This experiment 
conclusively proves that the same amount of vapor can exist 
in a space already filled with air as in a vacuum. The 
repulsive atoms of each however will be exerted against the 
sides of the vessel, and the resulting pressure will be the sum 
of the two; a fact which is proved by noting the height of 
the column e, which indicates the elastic pressure of the air 
in the globe before the vapor was admitted, and which, for 
example, we may suppose to be equivalent to the weight of 
20 inches of mercury. If we now open the stop-cock the 
mercurial column will be depressed by the additional repul- 
sion of the atoms of the vapor of water, and if the tempera- 
ture be at 75° (as we have previously supposed) the depres- 
sion will be 0*868 inches. 

The same result may be obtained by the following method, 
which also gives us an independent means of determining 
directly the amount of vapor which exists in the atmosphere 
at a given time, and which may be employed for verifying 
the results obtained by other means. Let a tight cask fur- 
nished with a stop-cock near its lower part be entirely filled 
with water, and let the small end of a tube which has been 
drawn out in a spirit lamp be cemented into the vent-hole 
above, so that no air can enter the cask except through the 
tube. Let this tube be filled with coarsely powdered dry 
chloride of calcium — a substance which has a great affinity 
for moisture — and the upper end put in connection with an 
open vessel containing air entirely saturated with moisture?, 
which can readily be effected by agitating a quantity of the 
liquid in the vessel from which the air is drawn. Let the 



230 WRITINQ3 OF JOSEPH HENRY. . [1855- 

stop-cock be now opened and exactly a cubic foot of water 
be drawn into a measured vessel; it is evident that precisely 
a foot of air will enter the top of the cask through the tube 
and between the interstices of the pieces of chloride of cal- 
cium, the moisture will be absorbed, and its weight can be 
accurately ascertained from the increase of weight of the 
tube and its contents, which had previously been weighed 
for that purpose. By this simple experiment as well as by the 
one we have previously given we are enabled to conclusively 
prove that the weight of vapor contained in the air in a 
given space is the same as that which would exist at the 
same temperature in a vacuum. To render the result of 
this experiment absolutely perfect however a slight correc- 
tion must be made on account of the expansion of the air and 
the vapor due to the increased repulsive energy of the com- 
pound over that of the air itself. This will be evident from 
a due consideration of what follows. 

If into an extensible vessel, such as an India-rubber bag 
filled with air, a little water be injected, the bag will be 
suddenly expanded by the additional repulsive force of the 
atoms of vapor. Previous to the introduction of the water, 
the bag will be pressed equally on the outside and on the 
inside ; on the former by the weight of the external atmos- 
phere, and on the latter by the repulsive or elastic force of 
the atoms of the inclosed air; when the water is introduced 
and a portion of it springs into vapor the elastic force of 
the aqueous atoms must be added to that of the atoms of 
the air, and the interior will then be pressed outward with 
a force equal to the sum of the two repulsions. For example, 
if the experiment be made at 60° and the air at its normal 
weight, the outward pressure within the bag previous to the 
introduction of the water will be equal to 30 inches of mer- 
cury, but after the water is injected it will be 30 and a half 
inches; hence expansion will take place and the bag will 
be distended until by the separation of the interior atoms 
the repulsion is so much weakened that the pressure with- 
out and within will again be equalized. The amount of 
the increase in bulk will be given by the following proper- 



-1859] WRITINGS OP JOSEPH HENRY. 231 

tion: as the pressure of 80 inches of mercury is to the pres- 
sure of 30J inches, so is the original bulk of the India-rub- 
ber bag to its bulk after the introduction of the vapor. 

From the preceding experiments and observations it is 
evident that in free air the vapor exists as an independent atmos- 
phere, being the same in weight and in tension as it woxdd he in 
a vacuum of the sarne extent and of the same temperature. That 
the same amount of vapor can exist in a space filled with 
air as in a vacuum at first sight appears paradoxical, but 
when we consider that a cubic inch of water expanded into 
steam at 212° occupies nearly 1,700 times the bulk which 
it does in the form of water, also that air may be compressed 
into a space many hundred times less than that of its ordi- 
nary bulk, it is evident that the extent of the void spaces 
is incomparably greater than the atoms themselves, and 
consequently it is not diflScult to conceive that the atoms 
of the vapor have abundance of space in which to exist 
between the atoms of air and the atoms of air between those 
of vapor. Dalton announces this important truth by stat- 
ing that air and vapor and almost all gases are vacuums 
to each other. This enunciation is a true expression of the 
state of diffusion which gases and vapors attain after the 
lapse of a given time, but it does not truly express the 
phenomena of the act of diffusion. In a perfect vacuum a 
given space is filled with vapor almost instantiineously, or 
with a rapidity which has not yet been estimated, but this 
is not the pame in a space already filled with air. In this 
case, though the vapor ultimately diffuses itself through 
the air as it would in a vacuum, yet time is required to pro- 
duce this effect; the result is as if there were a mechanical or 
some other obstruction to the free passage of vapor through 
the different strata of air, and indeed it would appear from 
the following experiments that a definite force similar to 
that produced by a slight attraction or repulsion is offered 
in the resistance of a given thickness of this medium: In 
the laboratory of the Smithsonian Institution a glass tube 
of about 3 feet in length, closed at its lower end, suspended 
vertically, and containing about an inch of water, has re- 



232 WRITINGS OP JOSEPH HENRY. [1B5S- 

mained for several years undisturbed in this condition with- 
out the least perceptible diminution in the amount of the 
liquid. In another experiment a pane of glass was removed 
from an external window of a room and the .place of the 
glass supplied by a board, through the middle of which a 
hole of about an inch in diameter was made, and in this 
opening a tube was placed horizontally, one end being in 
the room and the other in the outer air. To each end of 
this tube a glass bulb was attached, air tight, the one within 
the room containing about an ounce of water, while the tube 
and the bulb on the outside were occupied with air. The 
temperature of the air within the room was on an average 
about 70°, while that of the air without was on an average 
nearly 32°, and although the experiment was continued for 
several months during winter not one drop of water was 
distilled over into the outer bulb. When however the latter 
was surrounded by a freezing mixture a small quantity of 
vapor did pass over and was condensed into water ; and also 
when the vapor in the outer bulb was absorbed by introduc- 
ing a quantity of strong sulphuric acid into this bulb the 
water in the other bulb gradually diminished in weight. 

From these experiments it would appear that there is more 
than a mechanical obstruction to the transfusion of vapor 
through air, and that if the difference of tension of vapor in 
two vessels only amounts to a certain quantity no transfusion 
from one will take place to the other, or in other words for 
each inch or foot of thickness of a stratum of air a certain 
amount of unbalanced repulsive energy is required for trans- 
fusion. The rapid mingling of vapor with air is due in a 
considerable degree to the currents produced by the mixture 
itself and by variations of temperature. 

From an application of the principle relative to the co- 
existence of vapor and air, above given, we are able by means 
of tables A and B to immediately ascertain by inspection 
the amount of vapor which exists at any time and in any 
place in a foot of air perfectly saturated with moisture and its 
tension; that is, which contains as much vapor as it can 
hold at the given temperature. If for example the tern- 



-1859] W&ITINQS OP JOSEPH HENRY. 233 

perature of the saturated air be 75°, we would fiud opposite 
this, in table J5, (p. 225,) the weight of 937 grains; and by 
merely knowing the temperature at other times and at other 
places we would be able to determine the relative quantity 
of the vapor under these diflTerent circumstances and to form 
a judgment as to the dryness or humidity of different local- 
ities; but since there is a constant resistance to the diffusion 
of vapor through the atmosphere it follows that the air is 
seldom at any time or in any place entirely saturated. It 
is on the contrary in the condition of air filling a vessel into 
which less water has been injected than that necessary to 
furnish suflBcient vapor to fill the interstices between the 
atoms at the given temperature. 

We have been provided by Dalton with a very simple 
process by which the amount of vapor in a given portion of 
air which is not saturated can be determined. For this pur- 
pose it is only necessary to procure a bright metallic tum- 
bler, the thinner the' sides of which the better, and partly 
filling this with water at the temperature of the air and 
gradually adding colder water, stirring the mixture all the 
while with the bulb of a delicate thermometer, note the tem- 
perature at the moment when dew begins to be deposited on 
the outside. This temperature is called the dew-point, from 
which we determine by the tables the tension and the amount 
of vapor in the surrounding atmosphere. To render this 
clear, suppose the amount and tension of vapor in the atmos- 
phere to be that which would be produced by a temperature of 
60°, the temperature of the air at the time of the experiment 
being 70°, the atmosphere in this case would not be satu- 
rated; but if we should gradually cool it down to the tem- 
perature of 60°, it would then be saturated, and the least 
diminution of temperature below this degree would cause a 
precipitation of vapor in the form of mist or dew, and this 
is what really takes place in regard to tlie vapor which 
immediately surrounds the sides of the tumbler. The in- 
troduction of cold water into the tumbler cools the surface, 
which in turn cools the air immediately around it, and when 
the diminution of temperature reaches the point at which 



234 WRITINGS OF JOSEPH HENRY. [iteS- 

the air is just saturated the dew makes its appearance. 
Hence when the sides of the vessel are very thin the tem- 
perature noted by the thermometer within gives that of the 
dew-point without, and if wo inspect the table for this tem- 
perature we find at once the corresponding tension and 
weight of vapor in that portion of the atmosphere in which 
the experiment was made. 

It is not however upon the actual amount of vapor which 
the air contains at a given time or place that its humidity 
depends; but upon its greater or less degree of saturation. 
That air is said to be dry in which evaporation takes place 
rapidly from a surface of water or moistened substance. In 
an atmosphere entirely saturated with vapor, thftt is in one 
which is filled with as much vapor as the space which it 
occupies can contain, the vapor already in the air by its elas- 
tic force presses on the surface of the moist body and neu- 
tralizes the repulsive action of the water; if however the 
temperature be raised, the elastic force will be increased, 
and a new portion will be forced into the same space; the 
farther thei'efore the condition of any portion of air is from 
saturation the more rapid will be the evaporation from the 
moist bodies which it surrounds. 

For example, a portion of saturated air at a temperature 
of 102° would contain vapor of an elastic force equal to a 
pressure of 2 inches of mercury. (See table A, p. 217.) If 
the same air however contained vapor of only the elastic 
force of 59°, (that is if the dew-point were at 59°,) the elastic 
force would be half an inch, and consequently there would 
be a force unbalanced by the pressure of vapor equal to the 
pressure of a column of 1 J inches of mercury. The dryness 
therefore of the air is estimated by the difference of the 
elastic force of the vapor due to the temperature of the air, 
and of the elastic force due to the tension of the dew-point. 

In meteorological works generally, a portion of the atmos- 
phere contiiining vapor equal in tension to that of the tem- 
perature of the air is said to be fully saturated, and its 
humidity is marked 100; but if the elastic force of the air 
as determined by the dew-point is only one-fourth of that 



-1859] WRITINGS OP JOSEPH HENRY. 235 

necessary to produce complete saturation, the relative humid- 
ity is marked 25. To find then the relative humidity at any 
time, we seek from the tables the tension of vapor due to the 
temperature of the air, and again its tension due to that tem- 
perature to which it must next be cooled down in order to pro- 
duce precipitation, or full saturation, which temperature as 
we have seen is that of the dew-point. We then say, as the 
tension of the first temperature is to 100, so is the tension of the 
other temperature to the percentage of saturation. In this way 
comparative tables of relative humidity for diflTerent places 
are calculated from actual observation. 

Instead of employing the method of the dew-point for as- 
certaining the quantity of vapor in the atmosphere, a process 
which is attended with some diflBculty, particularly in cold 
weather, since in this case it is not easy to reduce the tem- 
perature of the water within the tumbler except by a freez- 
ing mixture suflBciently low to produce the deposition of dew, 
another process has been employed, called that of the wet 
and dry bulb thermometer. 

In this process we note the temperature of the air by an 
ordinary thermometer, and again we observe the tempera- 
ture to which in the same place a thermometer, whose 
bulb is covered with wet muslin, descends. If the air is 
perfectly saturated with moisture the two thermometers will 
indicate the same degree ; but if the temperature is above 
that due to the elastic force of the actual amount of vapor 
in the air the evaporation from the moist bulb will cause it 
to descend, by the absorption of heat, a certain number of 
degrees below that indicated by the naked bulb. 

M. Regnault has compared by direct experiment, the in- 
dications of the wet and dry bulb thermometer, with the 
actual amount of vapor contained in air at difiFerent tem- 
peratures and at different degrees of saturation, according 
to the method previously explained, and has in this way 
formed a series of tables by which the dew-point, the ten- 
sion of the vapor, and the weight in a cubic foot can be ascer- 
tained. In order however that these indications may be 
relied upon, it is necessary that the observations be made 
with care, since the evaporation from the wet bulb will very 



236 



WKinXGS OP JOSEPH HENRT. [0855-- 



much depend, as we shall presently see, apon the motion 
or stillness of the air ; and indeed we think that in all cases, 
in order to obtain comparable results, the balb should be 
fonned, so as in every instance to give the same amount of 
agitation to the surrounding medium. This will be evident 
from what we have said of the slow diffusion of vapor of fee- 
ble tension in the atmosphere. A local atmosphere of vapor 
is soon formed around the bulb, which very much impedes 
evaporation and consequently the reduction of temperature. 

Evaporaiion of water, — ^Water is constantiy evaporated 
from the surface of the ocean ; the amount however dimin- 
ishes as we proceed from the equator towards the poles. It 
is also exhaling from the surface of the earth, but in less 
quantities. The daily, monthly, and yearly amount of 
evaporation from a given surface of water and different 
kinds of earth is one of the most important data in reference 
to engineering and agriculture which can be furnished, and 
we would commend the research in reference to it to the 
special attention of any person who can command the time 
and desires an opportunity of advancing our knowledge of 
the operations of nature. A series of experiments on the 
evaporation from water may be made by carefully noting 
the quantity which disappears daily from a surface of a 
square foot freely exposed to air and sunshine. The depth 
of the box, which may be of tin encased in wood, should be 
6 inches, and the amount of water measured by a screw, the 
lower end of which tapers to a point, and on the upper end a 
divided circle is placed, so marked that the tenth part of the 
width of the screw or the one-thousandth of an inch may be 
estimated. Care should be taken to guard this surface from 
rain, and in high wind to estimate the amount of water 
which may be blown out ; the latter may be approximately 
found by surrounding the evaporating vessel with a border 
of gray paper, on which each drop of escaping water will make 
a stain ; the number and size of these spots being known, the 
amount of water blown out may be estimated from the re- 
sult of previous experiments in which the known quantity 
of the fluid has been sprinkled over the same surface. It is 
well, in order to make certain corrections, to observe the 



-1859] 



WRITINGS OF JOSEPH HENRY. 



237 



average temperature of the water during the day, and for 
this purpose a bulb of a thermometer is placed just below 
the surface of the liquid. In ascertaining the^ evaporation 
from diflTerent kinds of soil, a number of boxes of the dimen- 
sions above described, should be filled with different sam- 
ples, supplied with a measured quantity of water, weighed 
from day to day, and the loss (which will give the evapor- 
ating capacity) accurately noted. To ascertain the amount 
of evaporation from the actual surface of the earth in the 
course of the year, the loss should be daily determined from 
a new portion of earth taken from the surface in its actual 
condition. 

The annual amount of evaporation from a given surface 
of water in the interior of the country is greater than that 
of the rain which falls on the same surface, but the amount 
of evaporation from the surface of ground is generally less, 
particularly in mountainous districts. 

The evaporation does not depend upon the position of the 
evaporating surface since a piece of moist paper pasted on 
a pane of glass loses the same amount of water in the same 
time, whether it be held horizontally or vertically. It does 
however depend very much upon the nature of the surface; 
for example, less must be given oflF in a given time from a 
surface of salt water than from a surface of fresh water; and 
also from the cohesion with which water adheres to solids, 
a less amount of vapor is produced in a given time from a 
given surface of moist earth than from water, as is shown 
by the following table, deduced from observations made by 
M. Gasparin, in France, at temperatures from 73° to 75° 
P., during the time specified: 



Dates. 



1st day 


of August 


2d 


do. 


3d 


do. 


4th 


do. 


5th 


do. 


6th 


do. 


7th 


do. 



Evaporation 
from water. 



Inch. 
0-575 
534 
0-448 
0-4l>8 
0-450 
0-429 
0-367 



Evap<>rati<)n 
from earth. 



Inch. 
0-160 
0008 
0070 
0051 
0051 
0047 
0-051 



238 WRITINGS OP JOSEPH HENRY. [1B5S- 

Thc surface of the earth in this experiment was at first 
completely soaked with water. 

It is evident, on account of the slowness with which vapor 
diffuses itself through still air, that a much greater evapora- 
tion will be produced during a brisk wind, particularly if it 
be from a dry quarter, than during calm weather. If the 
vapor which is formed is allowed to accumulate over the 
evaporating surface, it will by its re-action retard the free 
ascent of the other portions of vapor; but if it be constantly 
removed as fast as it is formed the process will evidently 
go on more rapidly. 

Vapor as we have seen contains a large amount of latent 
heat, and water cannot be converted into an aeriform state 
without the supply of the necessary quantity of this princi- 
ple. Hence the higher the temperature, or the more freely 
the evaporating surface is supplied with heat, the greater 
will be the amount of vapor in a given time. 

We have seen that water immediately flashes into vapor 
in a vacuum, and we might infer from this that the rarer 
the air, or the more nearly it approximates to a void, the 
less obstruction would it offer to the free production of vapor, 
and the correctness of this inference has been satisfactorily 
shown by direct experiment. 

We owe to Dalton a series of precise experiments on 
the evajx)ration of water in airof different degrees of dryness 
and at different temperatures. He employed in his investi- 
gations a circular dish or pan 6 inches in diameter, about 
an inch deep, and suspended from the beam of a balance, by 
which the loss of water could be accurately ascertained from 
the variations of the weight in a given time. With this in- 
strument he made a series of experiments while the air con- 
tained different quantities of moisture, the amount of which 
was ascertained by means of the dew-point method we have 
before described in a perfectly still place and with the appa- 
rjitus exposed to a rapid draught of air. At the boiling point 
the evaporation in still air was 120 grains in a minute; in a 
gentle wind, 154 grains; and with a strong wind, 189 grains. 
A similar difference existed at the evaporating temperature 



-1859] WRITINGS OF JOSEPH HENRY. 239 

of 60° : in still air the evaporation was 21 grains in a minute ; 
in a gentle wind,'2'7; and in a strong wind, 3-3. From all 
the experiments he deduced the important result that the 
amount of evaporation in all cases is proportional to the 
difference of the elastic force of the temperature of evapora- 
tion and that of the dew-point or the vapor actually in the 
air. 

The empirical rule deduced from his table of results will 
serve approximately to calculate the amount of evaporation 
under the different conditions of temperature, dryness, &c., 
of the air, the temperature of the evaporating surface, and 
that of the dew-point being known. For still air multiply 
the difference of the tension of vapor due to the temperature 
of the evaporating surface, and of the vapor in the atmos- 
phere, by 4, and this will express in grains the weight 
of the vapor given off from a circular surface of water of G 
inches in diameter in one minute of time. If a gentle wind 
be blowing multiply the same difference by 5, and if a high 
wind exists during the experiment multiply the same differ- 
ence by 6. If for example the temperature of the evapo- 
rating surface be at the boiling point, and the temperature 
of the dew-point be 60°, we shall have 30 inches, the tension 
of the evaporating surface, and 0*5 for that of the tension of 
the vapor in the atmosphere at the time, the difference will 
be 29*5, which multiplied by 4 gives 118 grains. Again, if 
the temperature of the evaporating surface be 90, and that 
of the dew-point 70, then we shall have 1*4 — 0*7 = 0'7. If 
we suppose a gentle wind blowing at the time this must be 
multiplied by 5, and we shall have 07 X 5 = 3*5 grains as 
the amount of evaporation per minute from a circle of 6 
inches in diameter. 

The formula of Dalton, in the absence of other data, 
may be considered a valuable approximation; still results 
derived from direct observations in different parts of the 
earth, as we have said before, are desiderata of great value. 

Physical effects of vapor m tJie atmosphere, — Before consider- 
ing the more important meteorological changes produced in 
the general condition of the atmosphere by the vapor which 



240 WRITINGS OF JOSEPH HENRY. [1855- 

it contains, we may discuss some of the minor physical phe- 
nomena connected with the process of evaporation and the 
existence of water in an aeriform condition. 

Heat and moisture are the principal essential atmospheric 
agents in the production of vegetable matter, and where 
these are not found in suflScient quantities, however rich 
may be the soil in fertilizing materials, at least comparative 
if not absolute sterility must prevail. Unfortunately how- 
ever, these conditions though so highly favorable to the 
production of the substances which administer to the neces- 
sities and conveniences of life, are not equally favorable to 
the condition of health of the more highly civilized races of 
men. Heat and moisture are also the essential conditions 
under which the deadly malarious effluvia exert their bane- 
ful influence — especially upon the white race; and though 
science may hereafter furnish the means of disarming them 
of their terrors, yet at present they require the rich harvests 
of fields which would otherwise be uncultivated, to be reaped 
by the labor of individuals of another race so different in 
their physical organization as to be apparently exempt from 
the effects of these aerial poisons. The fertile rice, cotton, 
and sugar fields of the southern portion of the United States, 
are cultivated by negroes not only with impunity but with- 
out impairment of their phj'^sical enjoyments of life. 

The relative moisture of different countries is intimately 
connected with their condition as to healthfulness. While 
in the moist climate of Great Britain and that of some of the 
West India islands diseases of the lungs are prevalent, they 
are seldom known in the dry regions of Nebraska and Min- 
nesota. 

From the experiments of Dal ton, as we have seen, the 
rapidity of evaj)on\tion is proportional to the difference of 
elastic tension of the vapor in tl\e air and that of the evapo- 
rating surface. Meteorologists have generally adopted as the 
o.\prt.^ssionofrelativehumiditytheratiooftheforceofvaiK)rin 
the air to the force which it would have were it perfectly satu- 
rateil,or they sometimesadopt an equivalent expression by de- 
fining the relative humidity to be the ratio of the absolute 



-1859] WRITINGS OF JOSEPH HENRY. 241 

quantity of vapor which the air could contain at the given 
temperature, to that which it actually contains. According to 
this definition two places would bo equally damp which arc 
both half saturated with vapor, though the abstract quantity of 
vapor in the one case may be many times that of the other. 
Thus in winter when the temperature is very low and the 
absolute quantity of vapor in the air is exceedingly small, 
the air may have a maximum of dampness, that is to say, a 
very great relative humidity. Although this method of 
establishing the relative humidity of different places may 
correspond with variations in different phenomena, yet there 
arc some effects which appear to depend not on the relative 
but on the absolute amount of humidity in the air. The 
conducting capacity for electricity (for example) appears to in- 
crease with the absolute amount of vapor in the air, and hence 
experiments with the electrical machine succeed much better 
in winter than in summer, though the relative humidity in 
both cases may be the same. Again, since the temperature of 
our bodies is about 98°, and as this may be regarded as the 
temperature of an evaporating surface, the dififerenco of tcn- 
ision of vapor from the pores of the skin and that in the air 
must be very different in winter and in summer; and hencQ 
ill the latter case, when the dew-point a[)proaches the temper- 
ature of the body, we experience the sensation of the close- 
ness and sultriness of the atmosphere. 

On the other hand the intense cold which is felt on the 
Western plains in winter is due principally to the rapid evapo- 
ration from the pores of the skin — a result which can only 
be guarded against by a covering of close texture, such as 
the prepared skins of animals. In this connection we may 
mention a fact, which at first sight might appear to militate 
against the usages of civilized and refined life, namely, that 
dirt and grease are great protectors of the skin against in- 
clement weather, and therefore, says Mr. Galton, "the leader 
of a party should not be too exacting as to the appearance 
of his less warmly clad followers." Daily washing, if not 
followed by oiling, must be compensated by warmer clothing. 
A savage never washes himself in cold weather unless he 

16-2 



"242 WRITINGS OF JOSEPH HENRY. [1855- 

can give himself a clothing of grease. The tendency to 
evaporation from the skin during high winds must be op- 
posed by a substance which will partially close the minute 
orifices. Warmly clad and protected from the cold of winter 
the civilized man can enjoy the luxury of washing which 
is denied to the naked savage. 

Among other effects of evaporation connected with its re- 
duction of temperature, should be mentioned the advantages 
derived from draining marshy soil, that the cooling due to 
the evaporation of the surface water, is thereby diminished. 
It is said that the mean temperature of certain parts of 
England has been perceptibly increased by the general 
introduction of this system of agrieultural improvement. 

The moisture of the atmosphere often affects our health 
and comfort by its deposition on the walls and other parts 
of our habitations. It is absorbed with great force and in 
large quantities into the pores of almost every substance, and 
is given out again when a change in the temperature or dry- 
ness of the air occurs. Building-stone and brick absorb a 
large amount, which may be transmitted by capillarity from 
without through a wall of considerable thickness and evapo- 
rated at the interior surface. The dampness however of a 
stone house is not principally due to this cause, but to the 
deposition of moisture from the air on the cold surface of 
the wall — precisely analogous to the formation of dew on the 
surface of a pitcher containing cold water. 

If during a period of cold weather an apartment of a stone 
house has been closed, and on the recurrence of a warm day 
the windows are opened to air the room, the deposition we 
have mentioned takes place in abundance, and the result 
intended to be guarded against is promoted rather than 
diminished. If a fire be made in the room previous to open- 
ing the windows, so that the sides of the apartment may be 
made warmer than the air, the deposition will not take place. 
The effects both of the transmission and of the deposition of 
moisture can in a great measure be obviated by the means 
now generally adopted of lining the interior of the room 
with a thin coating of a non-conducting material separated 



-1859] WRITINGS OF JOSEPH HENRY. 243 

from the wall by a stratum of air. The surface of this 
material readily assumes the temperature of the air, and 
therefore does not allow of the deposition of much moisture. 
This internal lining, known by the name of furring, is 
usually composed of lath and plaster, but in some large 
buildings it is formed of a single thickness of brick, which 
prevents transmission of moisture from without, but does not 
fully obviate the tendency to deposition within, since a large 
amount of vapor is absorbed through the pores of the coat- 
ing of plaster into the substance of the brick and again 
given out with a change of temperature. 

The dampness of uewly-plastered walls is in part due to 
a chemical action, which (paradoxical as it may appear) is 
not obviated by heating the wall. After a newl}'^ plastered 
room has been dried by an excess of artificial heat, it con- 
tinues for a long time to give off vapor, and this is due to 
the chemical change going on while the lime in the plaster 
is in process of being converted from what is called a hydrate 
to a carbonate of lime. Perfectly dry slacked lime contains 
in chemical combination a portion of water, and when it is 
exposed to the atmosphere it absorbs carbonic acid from the 
air and expels the water in the form of vapor ; hence, after 
a plastered wall has been thoroughly dried it ought to bo 
exposed freely to currents of air, which niay furnish the car- 
bonic acid necessary to expel what may be willed the solid 
water or that of chemical combination. 

The water which is absorbed into the pores of stone by 
capillary attraction does not change its dimension. Mr. 
Saxton, of the Coast Survey, has shown that a rod of marble 
of 3 feet in length is not increased the ten-thousandth part 
of an inch by soaking it in water from a state of perfect dry- 
ness produced by heating it in an oven. The experiment 
was made on the marble of the Capitol, at the request of 
Captain Meigs, the superintendent of the extension of that 
national edifice. The absorption of moisture by organic 
substances however produces a change in their dimensions, 
which takes place with the exhibition of great force. The 
water is absorbed in great quantities at the ends of the 



244 wniTiNGs OP Joseph henry. [1855-- 

fibi*es of wood, and the principal expansion takes place 
in a direction at right angles to these fibres; it is also 
absorbed laterally between them, though in a less quan- 
tity. The warping of furniture is simply due to the ex- 
halation of the water in the form of vapor from the pores 
of the wood and the consequent shrinking of the part from 
which the exhalation has taken place, while the other parts 
retain their original bulk. To prevent this it is necessary 
to imprison the vapor by a coating of an impervious sub- 
stance, such as varnish or paint, or what is still better to 
expel the moisture by baking the wood and subsequently 
filling its pores with some resinous substance. It is impor- 
tant however to observe that when a substance is to be pro- 
tected from moisture by a covering of paint or varnish, care 
shoald be taken to cover every part with the impervious 
mixture, for the moisture may be drawn in through even a 
nail hole and pervade the whole interior capacity of the 
wood. 

Various instruments for indicating the moisture of the 
atmosphere without accurately measuring its changes have 
been constructed upon the principle of the absorption and 
consequent change of dimensions of diflferent substances. 
An instrument, which has lately been very widely described 
in the newspapers under the erroneous name of a simple 
barometer, is composed of two shavings of light wood glued 
together so as to make a ribbon of double thickness; the 
fibres of one layer being at right angles to those of the other. 
The absorption of the moisture into the shaving in which 
the fibres are lengthwise tends merely to increase the width 
and not the length of the compressed ribbon, while the 
absorption of moisture into the shaving of which the fibres 
are transverse tends to increase the length of the ribbon and 
thus causes it to curl. The foregoing instrument belongs to 
the class denominated hygroscopes, intended simply to in- 
dicate the changes which take place in the vapor in the 
atmosphere without furnishing the means of measuring its 
precise amount. For this purpose various substances are 
employed, such as a stretched cord, a human hair deprived 



-1859] WRITINGS OP JOSEPH HENRY. 245 

of oily matter by washing it in ether, and the beard of the 
wild oat; the change in length of the first two and the twist- 
ing of the latter furnish the indications required. 

Different materials absorb moisture in different degrees; a 
fact which is evident in passing along the sidewalk of a street 
at the beginning of a rain. While some of the bricks of 
which the pavement is composed are entirely wet at the sur- 
face others appear dry, because the water which has fallen 
upon them has been absorbed. It is scarcely necessary to 
add that after perfect saturation has taken place, and the 
surface is exposed to the heat of the sun, the appearance of 
wetness is exhibited in a reverse order. The relative absorp- 
tive power of different materials is frequently a matter of 
considerablepractical importance, which can be readily ascer- 
tained by weighing equal bulks of the material previously 
dried in an oven, and again after having been thoroughly 
soaked under the pressure of several feet of water. The 
absorption of water and its subsequent expansion by freezing 
is the most efficient agency in the gradual destruction of the 
architectural monuments by which the ancients sought to 
impress upon the future a material evidence of their power 
and wealth. 

CanstUution of clouds. — Water in the state of vapor (as has 
been stated,) is perfectly transparent, and this may be con- 
clusively proved, even of steam at a high temperature, by 
boiling water in a glass vessel with a long neck or by fasten- 
ing a glass tube to the spout of a tea kettle. The vapor 
within the glass will be entirely invisible, and that peculiar 
condition called doud will not be assumed till the transparent 
steam mingles with the cooler atmosphere and is partially 
condensed. The appearance of a cloud is also produced if 
a portion of transparent air is suddenly cooled, either by ex- 
pansion or mingling with a portion of air of a lower tem- 
perature. Much speculation has arisen in regard to the 
nature or condition of water when in the intermediate state 
of cloud, and though the subject has occupied the attention 
of scientists for more than a century it is still not fully settled. 

Saussure, the celebrated Swiss meteorologist, states that in 



246 WRITINGS OP JOSEPH HENRY. [1855- 

ascending the sides of a mountain into the region of the 
clouds he has seen globules of water as large as small peas 
floating in the air, which from their levity were evidently 
hollow spheres, similar to small soap bubbles. From this 
observation the idea became prevalent that the water of a 
cloud was in a vesicular condition, or in other words that 
cloud consists of minute hollow spheres of liquid water filled 
with air which is rendered more buoyant by the rarefaction 
due to the heat of the sun ; and this opinion was strengthened 
by the fact that clouds do not give a decomposition of the 
rays of light suflScient to exhibit the phenomena of the rain- 
bow. In what manner such a condition of water can be 
produced and how it can be retained, has not, so far as we 
are informed, been explained by any principle of science. 
A soap bubble soon becomes too thin to retain its globular 
form, and is resolved into the condition of soap water. Ordi- 
nary water is still more unstable and cannot bo retained for 
an instant in a hollow spherical form. We shall therefore be 
on the safe side if we adopt an hypothesis apparently more 
in accordance with known and established principles, and if 
this does not furnish a logical account of all the phenomena 
we must wait until further research or light from collateral 
branches of science dispels the obscurity with which this 
point may be involved. 

The suspension of the clouds can be explained by taking 
into account the extreme minuteness of the particles of which 
they are composed. In the case of mists which are some- 
times formed at the surface of the earth and afterwards be- 
come clouds in being elevated into the atmosphere by a wind 
blowing between them and the earth, the particles are of such 
extreme tenuity as to be invisible to the naked eye, and their 
presence is rendered evident only by looking through a 
stratum of considerable thickness. 

If particles of lycopodiura (the sporules or seeds of the club- 
moss) are dusted upon a flat glass they exhibit a series of colors, 
when held between the eye and the light, produced by the inter- 
ference of the waves of different rays of light. In order to pro- 
duce this effect, the particles of lycopodiurn (as can be proved 



-1859] WRITINGS OP JOSEPH HENRY. 247 

mathematically) must not exceed the seven-thousandth of 
an inch in diameter. Now the particles of a cloud are 
sometimes known to present the appearance of similar colors, 
and therefore are not larger than those of the lycopodium. 
This extreme minuteness is sufficient to account for the sus- 
pension of clouds or the extreme slowness with which they 
descend. M. Maille of Paris has attempted to compare the 
volume of a particle of this size with that of a drop of rain 
water of about a tenth of an inch in diameter. He finds that 
it would require upwards of 200 millions of particles of cloud 
to make one drop of rain water of the size mentioned. We 
are prepared to admit the correctness of the conclusion when 
we reflect on the rapid increase of the volume of a sphere 
relative to the increase of its diameter. For example, if a 
series of spheres have diameters in the ratio of 1, 2, 3, 4, 5, 6, 
the volumes or weights of the spheres, provided they are of 
homogeneous material, will be represented by the numbers 
1, 8, 27, 64, 125, 210. Indeed nothing is more deceptive than 
the estimate we form of the relative volume or weight of 
difierent solids by simply comparing their diameters. It 
requires but a very small increase in the diameter of an egg, 
for example, to double its weight. We know that the re- 
sistance of the air to the descent of a falling body is in 
proportion to the surface which it presents to the resisting 
medium. Now every time a drop of water is divided, a new 
surface is exhibited, and when the division is carried as far 
as that of the particles of cloud, the resistance must be so 
great that an indefinite length of time must be required to 
produce a descent of a few hundred feet. 

The process of the formation of clouds will be described in 
a Subsequent section ; we may here however mention that 
the forms and aspects in which they are presented are indic- 
ative of the circumstances in which they are forming or dis- 
sipating, and hence the importance of giving special names 
to these forms in order that they may become objects of defi- 
nite study. The first attempt at a descriptive classification 
of clouds was by Mr. Luke Howard in 1802. An account of 
this is given in all works on meteorology, and we need here 



248 WRITINGS OF JOSEPH HENRY. [1855-r 

only give a brief exposition of his nomenclature. Ho divides 
clouds into three primarj^ modifications: cumulus, stratus, 
and cirrus, with intermediate forms passing into one another 
under the names cumulo-stratus, cirro-stratus, cirro-cumulus; 
and lastly, a composite form, resulting from a blending or 
confusion of the others, under the name cirro-cumulo-stratus 
or nimbus. 

1. Cirrus, consisting of parallel or diverging fibres, ex- 
tended by increase of material in any or in all directions. 

2. Cumulus, convex or conical masses, increasing upward 
from a horizontal base. 

3. Stratus, a widely extended continuous horizontal Bheet 

4. CirrO'Cumvlus, generally known as " mackerel sky," con- 
sisting of small rounded masses, disposed with more or less 
regularity and connection. 

5. Cin'o-8<ra<M8, consisting of horizontal or slightly inclined 
masses, undulating or separating into groups, giving the idea 
of a shoal of fish in the distance. 

6. CamvlO'Stratus consists of a blending of the cirro-stratus 
with the cumulus. 

7. Ninribus is the cloud from which a. continued rain falls. 

A drawing of these diflferent forms of clouds will be found 
in the instructions for meteorological observations published 
by the Smithsonian Institution. 

Dew and hoar frost — When a mass of moist air is brought 
in contact with a cold body its vapor is condensed into water 
and deposited in minute globules on the cooled surface, which 
constitute dew. If the temperature of the surface is below 
the freezing point the globules of water will be frozen \\\^o 
minute crystals of ice, which constitute hoar frost. For a 
long time the nature of these phenomena was entirely mis- 
conceived ; the effect was put for the cause, the dew being 
regarded as producing the chill which accompanies its for- 
mation instead of the reverse. Dr. Wells of London, born in 
South Carolina, was the first who gave the subject a scien- 
tific investigation, and by a series of ingenious, accurate and 



-1859] WRITINGS OF JOSEPH HENRY. 249 

conclusive experiments furnished a definite explanation of 
all tlie phenomena. They are simply due to the cold pro- 
duced in different bodies by radiation. As we have seen, the 
earth is constantly radiating heat into celestial space, and is 
constantly receiving it from the sun during the continuance 
of that body above the horizon. As long as the heat from 
the sun exceeds that radiated into space the temperature of 
the surface of the earth and that of the air in contact with it 
continues to increase; but when the two are equal the tem- 
perature remains stationary for a short time and then begins 
to decline as the heat of the sun, on account of the obliquity 
of the rays, becomes less than the radiation into space. The 
maximum of heat generally takes place between 2 and 3 
o'clock in the afternoon, and the cooling from this point 
goes on until near sunrise of the next morning. As soon as 
the sun descends below the horizon the cooling of the surface 
of the earth takes place more rapidly if the sky be clear; the 
air in contact with grass and other substances which are 
cooled by this radiation will deposit its moisture in a manner 
analogous to that of the deposition of water on a surface of 
a metallic vessel containing a cold liquid. Although the 
atmosphere may contain the same amount of vapor, yet the 
quantity of dew deposited during the night in different 
places and on different substances is very unequal. It is 
evident that it must depend to some extent upon the 
quantity of moisture, since if the air were dry, no deposi- 
tion could take place; and indeed it has been remarked that 
on some parts of the plains west of the Mississippi dew is 
never observed. It must also depend upon the clearness of 
the sky; for if the heavens be covered with a cloud the 
radiant heat from the earth will not pass off into celestial 
space, but will be partly absorbed by the cloud and radiated 
back to the earth. This is not a more hypothesis but has 
been proved by direct experiment. The author of this article 
while at Princeton some years ago placed a thermo-electric 
apparatus in the bottom of a tube provided with a conical 
reflector, and thus formed, if the expression may be allowed, 
a thermal telescope, with which the heat of a cloud of the 



250 WRITINGS OF JOSEPH HENRY. [1855- 

apparent size of the moon was readily perceptible.* When 
this instrument was directed first to the clear sky in the 
vicinity of a cloud, and then immediately after to the cloud 
itself, the needle of the galvanometer attached to the thermo- 
electric pile in the tube always deviated several degrees. At 
first sight it might appear from this experiment that the heat 
of the cloud was greater than that of the transparent air in 
which it was floating, but this was not necessarily the case; 
the rays of heat from the apparatus when it was directed into 
the clear sky passed oflF into celestial space, while when the 
instrument was directed to the cloud they were absorbed and 
radiated back. It is probable however that the lower surface 
of the cloud is really a little warmer than the air in which 
it is floating, from the radiation of heat by the earth, while 
the upper surface is probably colder on account of the un- 
compensated radiation into space. But be this as it may, the 
counter radiation of the clouds prevents the suflScient cool- 
ing down of the bodies at the surface of the earth for the 
deposition of dew, or at least for the formation of a copious 
quantity. A haziness of the atmosphere (and it is prob- 
able a large amount of invisible vapor) will retard the 
radiation, and hence a still, cloudless night, without a depo- 
sition of dew, is considered as indicative of rain. The 
amount of deposition of dew will also depend upon the still- 
ness of the atmosphere ; for if a brisk wind be blowing, the 
diflerent strata of air will be mingled together, and that 
which rests upon the surface of the ground will be so quickly 
displaced as not to have time to cool down sufficiently to 
produce the deposition. 

Again the deposition will be more copious on bodies the 
surfaces of which are most cooled by the radiation. It is 
well known that different substances have different radiating 
powers. The following table from Becqucrel exhibits the 
proportional tendency of different substances to promote the 
deposition of dew. The figures do not represent the relative 
einisssive power, but the combined effects of emission and 
conduction : 

*[Sec a7itCj vol. i, p. 28.'!.] 



-1859] WRITINGS OF JOSEPH HENRY. 251 

1. Lampblack 100 

2. Grasses 103 

8. Silicious sand 108 

4. Leaves of the elm and poplar 101 

6. Poplar sawdust 99 

6. Varnish -. - 97 

7. Glass — 98 

8. Vegetable earth 92 

Polished metals are of all substances the worst radiators; 
they reflect the rays of heat as they do those of light, and it 
would appear that the escape of heat from the substance of 
the metal is prevented by internal reflection. In order that 
the surface of a body should cool down to the lowest degree 
it is necessary that it should be a good radiator and a bad 
conductor, particularly if it be in a large mass and un-in- 
sulated. Thus the surface of a mass of metal coated with 
lamp black, though it radiates heat freely, will not be as 
much cooled under a clear sky as a surface of glass, since 
the heat lost at the surface is almost immediately supplied 
by conduction from within. If however a very small quan- 
tity of metal such as gold leaf be suspended by fine threads, 
the dew will be deposited, because the heat which is radiated 
is not supplied by conduction from any other source, and 
hence the temperature will sink to a low degree. 

M. Melloni has within a few years past repeated the experi- 
ment of Wells, and established the correctness of his conclu- 
sions ; and has also added some particulars of interest. He 
found that the apparent temperature of the grass, which in 
some cases was 8°or 10° lower than that of the air at the height 
of 3 or 4 feet, was not entirely due to the actual cooling of the 
air to that degree, but to the radiation and cooling of the 
thermometer itself, the glass bulb of which is a powerful radi- 
ator. To obviate this source of error in estimating the tem- 
perature he placed the bulbs of his thermometer in a small 
conical envelope of polished metal of about the size of an 
ordinary sewing thimble. This prevented a radiation and 
by contact with the air indicated its true temperature. He 
found with thermometers thus guarded that the solid body 
was in no case cooled down more than 2° below the temper- 



252 WRITINGS OF JOSEPH HENRY. [1855- 

ature of the surrounding air, and that the amount of radia- 
tion was nearly the same at all temperatures.. The explana- 
tion therefore of the great cold of the air between the blades 
of grass is as follows: By the radiation of the heat the grass 
is at first cooled two degrees lower than the air at the sur- 
face of the earth, and next the thin stratum of air which 
immediately surrounds the grass is cooled by contact to the 
same degree. It then sinks down and another portion of 
air comes in contact with the blade of grass, and is in its 
turn cooled to the same extent, and so on until all the air 
between the blades is two degrees lower than that of the air 
farther up. The radiation however continues, and a stratum 
of air from the mass already cooled is cooled two degrees 
more, which sinks down as before, and so on until the air 
between the blades is cooled to 4° below its normal condi- 
tion ; and in this way the process may be continued until 
the temperature descends to 8° or 10° below that of the strat- 
um of air a few feet above. In this way we can readily ex- 
plain the small amount of dew deposited on the tops of trees, 
since the air as soon as it is cooled sinks down toward the 
ground, and its place is continuously supplied by new por- 
tions of the atmosphere. To the same cause we may at- 
tribute copious deposition of dew on wool and other fibrous 
materials which, though they do not radiate heat more freely 
into space, yet entangle and retain the air between their 
fibres, and thus allow the cooling process we have described 
lo go on. It would appear that spider-webs radiate heat 
freely into space, since they are generally covered with a 
large amount of dew; their insulated position prevents them 
from renewing their heat, but according to the above prin- 
ciple a much larger amount of deposition ought to be pro- 
duced by the same material were it loosely gathered up into 
a fibrous mass. The fact of the screening influence of the 
clouds teaches us that a thin cloth or even a slight gauze 
supported horizontally over tender plants is sufficient to 
neutralize the radiation and to prevent injury from frost 
during the clear nights of spring or autumn. The same 
effect is produced by artificial clouds of smoke. 



-1859] WRITINGS OF JOSEPH HENRY. 253 

Since radiation from the surface of the earth is most in- 
tense on clear nights, when the moon is visible, many of the 
effects which are due to this cause have been referred to 
lunar influence; for example, a piece of fresh meat exposed 
to the moonlight is said to become tainted in a few hours; 
this may arise from the deposition of moisture on the surface 
of the meat due to the cooling from radiation. The moon 
itself however acts as a cloud and radiates back to the earth 
a portion 6f the heat which it received from the earth as 
well as a portion of that which it received from the sun ; 
and hence Sir John Herschel has referred to this cause, with 
apparent probability, the origin of an assertion of the sailors 
that "the moon eats up the clouds." He supposes that they 
may be dissipated by the radiant heat from that body, which 
being of low intensity and but feebly penetrating the lower 
stratum of the atmosphere may serve to dissipate the clouds. 
Though a wrong explanation is generally given by the pop- 
ular observer of natural phenomena, and though effects and 
causes are frequently made to change places in his explana- 
tions, yet it is true, as Biot has properly said, that the scien- 
tist who devotes himself assiduously to investigate the sub- 
ject of popular errors will find in thcin a sufficient amount 
of truth to fully repay him for his labor. 

Formation of fogs, — ^The difference between a fog and a 
cloud relates' principally to the conditions under which they 
are severally formed. A fog has been aptly called a cloud 
resting on the earth and a cloud a fog suspended in the 
atmosphere. The circumstances under which a fog is usually 
produced are the following: Either the surface of the earth 
or water is warmer than the air or it is cooler. If the tem- 
perature of a river or of a damp portion of ground is higher 
than that of the atmosphere which rests upon it the warmer 
surface will 'give oflF vapor of an elastic force due to its tem- 
perature. Should the superincumbent air be extremely dry 
the vapor will diffuse itself up through it in an invisible 
form without condensation, and no fog will be formed until 
by the continuation of the process the air becomes completely 
saturated; and then if an excess of heat remain in the evapo- 



254 WRITINGS OF JOSKPII HENRY. [1855- 

rating surface the fog will bo produced, and will increase in 
density and height so long as a difference of temperature 
continues. If however a wind be blowing at the time, so 
that successive portions of unsaturated air are brought over 
the place, no fog will be produced. A still atmosphere there- 
fore is a necessary condition to the accumulation of fog. 

The foregoing is the usual method in which fog is pro- 
duced, for it is well known that in cold weather the surfaces 
of lakes and rivers are much warmer than the stratum of air 
which rests upon them. 

It is however frequently observed that fogs are formed 
during still nights in low places when the surface of the 
ground is colder than the stratum of the atmosphere which 
rests upon it, and indeed we have shown that the tempera- 
ture of the surface of the earth on a still and clear night is 
always lower than that of the air which is immediately in 
contact with it ; and it is not easy, without further explana- 
tion, to see the reason why fogs should not always be pro- 
duced in this case as well as dew. When the atmosphere is 
still the condensation of the vapor by the coldness of the 
surface is so gradual that the air is not disturbed, and the 
stratum immediately above the grass has relatively less mois- 
ture in it than that a few yards higher ; hence no fog ought to 
be produced in this case, since all the precipitation produced 
is that which has settled directly upon the grass in the form 
of dew. In this case we may define the dew to be a fog 
entirely condensed into drops of water. The question still 
arises how under these circumstances can a fog really be pro- 
duced. The answer is that another condition is required, 
namely that the surface cooled by radiation should slope 
to a lower level, as in the side of a hill or the concave surface 
of the sides of a hollow. In this case the superincumbent 
stratum of air of which the temperature has been lowered 
by contact with the cold earth, flows down the declivity by 
its greater weight into the valley below, and there mingling 
with the damp air which generally exists in such places, 
precipitates a part of its transparent vapor into visible fog. 
In this manner large hollows are sometimes seen in the morn- 



-185d] WRITINOS OP JOSEPH HENRY. 255 

ing filled with a mass of fog, exhibiting a definite and level 
surface presenting the appearance of a lake the shores of 
which are the surrounding eminences; and if a depression 
of sufficient depth occurs in any part of the circumference of 
the basin, through this the fog is seen to flow like a river 
from the outlet of a lake. 

The explanation we have here given of the formation of 
fog in low places is also applicable to the phenomenon fre- 
quently observed of early frost in the same localities. As 
rapidly as the air is cooled on the sides of sloping ground it 
sinks into the valley below and its place is supplied by the 
warmer air above, which has not been subjected to the cooling 
influence. In the vicinity of Washington the hollows are 
sometimes found several degrees oolder than the more ele- 
vated parts of the surrounding surface. Fogs are produced 
on the ocean when a gentle wind charged with moisture 
mingles with another of a lower temperature. The wind 
from the Gulf Stream mixing with the cold air which rests 
upon the water from the arctic regions, (which as before 
stated flows along close to the eastern shores of our con- 
tinent,) gives rise to the prevalence of fog over the Banks of 
Newfoundland. 

There is another atmospherical phenomenon which though 
it does not affect the hygrometer and is only indirectly con- 
nected with moisture, is generally classed with fogs. I allude 
to what is called dry fog — a smoky haziness of the atmos- 
phere, which frequently extends over a large portion of the 
earth. The nature of these fogs is now pretty well under- 
stood, and more refined observations, particularly with the 
microscope, have served to dissipate the mystery in which 
they were formerly enshrouded. When a portion of the air 
in which the fog exists is filtered through water and the sub- 
stance which is retained is examined by the microscope it 
is found to consist of minute fragments, in some cases of 
burnt plants, and in others of the ashes of volcanoes. It is 
surprising to what a distance the pollen of plants and minute 
fragments of charred leaves may be carried. Samples of sub- 
stances which have been collected from rain water and ex- 



256 WRITINGS OF JOSEPH HENRY. [18S5- 

amined microscopically by Professor G. C. SchaeflFer of Wash- 
ington, at the request of the Smithsonian Institution, have 
been found to consist of portions of plants which must have 
come from a great distance, since the species to which they 
belong are not found in abundance in the localities at which 
the specimens were obtained. It is highly probable that a 
portion of the smoke or fog-cloud produced by the burning 
of one of our western prairies is carried entirely across the 
eastern portion of the continent to the ocean. Oa this sub- 
ject Dr. Smallwood communicated a series of interesting 
observations to the American Association at their meeting 
in Albany in 1855. Particles of matter of the kind we have 
described are good absorl^ers and radiators of heat, and hence 
in the daytime they must become warmer than the surround- 
ing atmosphere and tend to be buoyed up by the expansion 
of the air which exists in the interstices between them, while 
at night they become cooler by radiation than the surround-' 
ing air and tend to condense upon themselves the neigh- 
boring moisture, and consequently to sink to a lower level. 
It is on this account that the smoky clouds which are pro- 
duced by the enterprising manufacturing establishments of 
Pittsburg and other western cities, sometimes descend in still 
weather to the surface of the earth and envelop the inhabi- 
tants in a sable curtain more indicative of material prosper- 
ity than of domestic comfort. From the density and the 
wide diffusion of these smoky clouds they must produce a 
sensible eflFcct upon the temperature of the season of the year 
in which they occur. During a still night, when a cloud of 
this kind is over head, no dew is produced; the heat which 
is radiated from the earth is reflected, or absorbed and radi- 
ated back again, by the particles ©f soot, and thus the cooling 
of the earth necessary to produce the deposition of water in 
the form of dew and hoar frost is prevented. 

So well aware of this fact are the inhabitants of some parts 
of Switzerland that, according to a paper by Boussingault, in 
a late number of the Amiales de Chimie, they kindle large 
fires in the vicinity of their vin© fields and cover them with 
brush to produce a smoke-cloud by which to defend the 



-1859] WRITINGS OF JOSEPU IIENUY. ^257 

tender plants from the effects of an untimely frost. Though 
the first announcement of the proposition by some of our 
earlier meteorologists that the peculiar condition of the at- 
mosphere known as " Indian summer " might be produced by 
the burning of the prairies, was not thought deserving of any 
comment, yet the advance of science in revealing the facts 
just stated renders this hypothesis by no means unworthy 
of attention. A large amount of smoke existing in the atmos- 
phere must have a very sensible effect in ameliorating the 
temperature of the season by preventing the cooling duo to 
radiation ; and although this may not be tlie sole cause of the 
peculiarity of the weather above mentioned, it may be an im- 
portant consideration in accounting for the smoky appear- 
ance of the air and the eflfect produced upon the eyes. 

In concluding this section we would commend to the atten- 
tion of the microscopists of this country, — ^as a readily accessi- 
ble and interesting field of research, — the subject of atmos- 
pheric dust. The atmosphere constantly holds in suspension 
a mass of particles derived from the mineral crust of the 
globe and from animals and vegetables, which by being 
deposited in undisturbed positions, serves as a record to bo 
read by the microscope of changes alike interesting to the 
antiquarian and the naturalist. On this subject M. Pouchct 
has lately presented a paper to the French Academy of 
Science, in which he enumerates the particles of mineral, 
animal, and vegetable origin which he has found deposited 
from the atmosphere. Under the latter he mentions specially 
particles of wheat flour which have been found as an ingre- 
dient of dust in tombs and vaults of churches undisturbed 
for centuries. The dust floating in the atmosphere may 
readily be collected by filtering the air through a tube swelled 
in the middle, bent into the form of a syphon, partly filled 
with water and attached at the lower end to the vent-hole 
of a cask from which water is drawn, or simply by sucking 
through the air by means of the mouth. 

Rain. — ^The discussion of the rationale of the production of 
rain will be given in a subsequent part of this article. We 
shall in this place however state some facts in regard to it 

17-2 



258 WRITINGS OF JOSEPH HENRY. [1855- 

which are naturally connected with the general subject of 
the existence of vapor in the atmosphere. 

The humidity so constantly supplied to the air by evapora- 
tion is returned to the surface of the earth principally in the 
form of rain resulting from the union of the very minute 
particles of water wh ich constitute the mass of clouds. With- 
out stopping to ipquire into the cause of union in this place 
we may remark that we think it probably due to the further 
condensation of the vapor which first assumed the condition 
of a cloud. Rain, it is true, has been observed to fall from 
apparently a cloudless sky, but the occurrence is one of ex- 
treme rarity, and it seems possible that it is brought from a 
distance by wind at a high level. 

A knowledge of the quantity of rain which falls in diflfer- 
ent portions of a country is important, not only with refer- 
ence to agriculture, but also with reference to internal 
navigation, as well as to the application of hydraulic power, 
the occurrence of devastating floods, the water supply of 
cities, and the sanitary condition of a district. 

Almost every portion of the earth on which rain falls is 
provided with natural drains that 'carry off the surplus 
water (above that which evaporates) to the ocean whence it 
came; and taking the earth as a whole the same amount of 
water must be returned to the ocean as was taken from it by 
evaporation. 

Nearly the whole surface of the earth is divided into 
basins, each provided with a separate system of drainage. 
The boundaries of these basins can readily be traced on the 
map by drawing a line around between the heads of the 
streams, the waters of which find the level of the ocean 
through the channels of different rivers. Thus we have the 
gieat primary basins of the Amazon, the Mississippi, and the 
St. Lawrence, and the secondary basins of the Ohio, the Mis- 
souri, and the Tennessee, giving the latter name to those 
which pour their waters not into the ocean but into another 
river. 

A knowledge of the amount of rain which falls on each of 
the subordinate basins supplying a river like the Mississippi 



-1859] WRITINGS OF JOSEPH HENRY. 259 

with the water which passes through it into the ocean, if 
transmitted by means of the telegraph, would be of the 
greatest value, in connection with previous experience as to 
the elevation of the water of the river corresponding to a 
given indication of the rain-gauge, in furnishing the means 
by which the eflfects of floods may be guarded against and 
the labors of the husbandman along the banks preserved, 
in many cases, from destruction. A single gauge in each 
subordinate basin would be sufficient to furnish valuable 
practical information of this kind, and in the case of the 
Mississippi River, (especially if applied to the basins on the 
eastern side,) would suffice to give premonitory indications of 
a sudden rise at the lower part of the river, since the water 
which is furnished from the western part of the valley of the 
Mississippi is morecpnstant in its amount, or in other words 
not so subject to fitful variations. 

The simplest method of measuring the rain, which any 
one may practice for himself, is to catch the water in a cylin- 
drical vessel, like an ordinary tin pail, and to measure the 
depth in inches and tenths of an inch after each shower. It 
is hardly necessary to remark that the vessel should be so 
placed that it may not be screened by trees, buildings, and 
other obstacles from the wind which bears along the falling 
drops. The object of the investigation is to ascertain thQ 
number of inches of water which fall from the clouds on a 
given space in a given time — for example, a year or a season. 
It is well known that while the wind is blowing strongly 
the drops descend in an oblique direction, and gauges have 
been proposed which, by the action of the wind, would so 
incline their mouths as always to present them at right 
angles to the direction of the drops ; but gauges of this kind 
would not give the indication required, which is that of the 
absolute quantity of rain which falls on a given horizontal 
extent of the surface of the earth. 

A remarkable fact has been observed as to the amount of 
rain collected at diflferent heights. It is a well known phe- 
nomenon, of which we shall give the explanation hereafter, 
that on the windward side of a mountain a greater amount 



260 WRITINGS OF JOSEPH HBNRY. [1855> 

of rain falls annually than at a less height on an extended 
plain. The eflFect however, to which we now refer, is just 
the reverse, since it is found that less rain falls on the top 
of a tower, and even of an ordinary building, than at the 
bottom. This phenomenon is due in part at least to the 
fact that a drop in its descent through a foggy atmosphere, 
in which the rain is falling, catches in its path all the min- 
ute particles of water between the upper and lower stations. 
It cannot be due, except in a slight degree, to the condensa- 
tion of the transparent vapor in the atmosphere which oc- 
cupies the line of its descent, since the condensation of this 
would rapidly heat the drop of water, although its tempera- 
ture were considerably lower than that of the air, on account. of 
falling from a colder region. The principal cause of the dif- 
ference is to be found in the effect of the wind in passing over 
and around the edifice on which the gauge is placed. The 
effect of this cause was first investigated by Professor Bache, of 
the United States Coast Survey, who made a series of obser- 
vations with a number of gauges placed on diflferent sides of 
the roof of a shot tower in Philadelphia. He found that dif- 
ferent quantities of rain were collected by gauges thus placed. 
To explain the effect of the wind, we may refer to what 
takes place when an obstacle like that of a large stone is found 
with its upper end just below the surface of a running stream. 
The water of the current will pass over and around the stone, 
and will rise above the general surface ; there will exist a ten- 
dency to a partial vacuum on the sheltered side; the liquid 
in passing over and around the stone will be accelerated ; 
the particles of water which pass around the stone, sup- 
posing it to be a cylinder, will traverse a space equal to the 
semi-circumference of the circle, while those moving along the 
general current, and not deflected, will pass through a space 
equal to the diameter of the same circle. A similar effect 
would be produced by the wind striking against a tower. 
The portion which passes around the top will be accele- 
rated ; that which strikes against the top will be deflected 
upward, and in both cases a diminution in the quantity of 
rain which falls on the top of the tower will be the result. 



-1859] WRITINGS OF JOSEPH HENRY. 261 

Suppose the wind is coming from the west, and striking with 
force against the side of the tower which faces that direction, 
it will be deflected upward, and thus retard the fall of rain 
on the near side of the roof of the tower, and precipitate it 
over the leeward side, while the portion of wind which passes 
around the circumference of the tower, near its top, will be 
accelerated, and will by the latter action impart its motion 
to the air on the north and south sides of the roof of the 
tower, which will cause the drops of rain to be crowded to- 
gether on the leeward side. 

The effect of the upward deflection of the wind and the 
acceleration of the rain, under conditions such as we have 
just described, are strikingly illustrated by the observations 
which were made on the high tower of the Smithsonian In- 
stitution. Three gauges were placed on the roof of this 
tower, — one on the west, one in the centre, and a third on 
the east side. Now if the prevailing wind be west, we should 
expect (if the theory which we have presented is correct,) that 
the west gauge would contain the smallest quantity of water, 
the middle one next, and the one oa the east side the great- 
est; and this was found to be actually the case. 

The action of the wind also materially affects the amount 
of water which falls in different gauges of different forms 
and sizes at the surface of the earth. It is well known that 
different gauges, which indicate the same amount of rain in 
calm weather, differ materially in the quantity of water 
which they collect in high winds. If the gauge be of con- 
siderable size, and project above the surface of the earth, the 
air will be deflected upward and accelerated around it, as in 
the case of the tower; nor is this result obviated by sinking 
the large gauge to the level of the earth, since in that case 
the current curves down into the gauge and tends to carry 
out a portion of the falling drops on the opposite side. From 
a series of experiments made at the Smithsonian Institution, 
and continued for several years, it is found that a small 
cylindrical gauge, of 2 inches in diameter, and about 6 inches 
in length, connected with a tube of half the diameter, to re- 
tain and measure the water, gives the most accurate results. 



262 WRITINGS OF JOSEPH HENRY. [1855- 

In still weather it indicates the same amount of water as the 
larger gauges, but when the wind is high it receives more 
rain, for on account of its small size the force of the eddy 
which is produced is much less in proportion to the momen- 
tum of the drops of water. This gauge, which has been 
copied from one introduced by Mr. James Stratton, of Aber- 
deen, may be still further improved by cutting a hole of the 
size of the cylinder into a circular plate of tin of 4 or 5 inches 
in diameter, and soldering this to the cylinder like the rim 
of an inverted hat, three or four inches below the orifice of 
the gauge. 

The effect of the wind in disturbing the level of light snow 
in the vicinity of buildings illustrates the general princi- 
ples which we have endeavored to explain. When a rapid 
current of air is obstructed by a building the acceleration 
of its velocity on the side of the eddy is marked by the re- 
moval of the snow to a considerable distance. Indeed all 
the phenomena we have mentioned in regard to rain are 
illustrated by the extraneous motion given to the particles 
of descending snow. 

Constitution and phenomena of the compound aJtmosphere. — 
From the principles we have endeavored to explain, we may 
now readily infer what would be the general effects if the 
earth were surrounded with an ocean of water and devoid 
of an atmosphere. At first sight it might appear that all 
the water of the ocean would immediately pass into vapor ; 
but, on a little reflection, it will be seen that this would not 
be the case. A definite amount of vapor would be formed, 
which by its pressure on the surface of the water would pre- 
vent any further evaporation, provided the whole globe and 
the space around it were of uniform and constant tempera- 
ture. 

A portion of vapor would rise from the water and would 
expand as it rose until the upper atoms were so far separated 
that their repulsion would become insensible and they would 
be retained as an appendage to the earth merely by their 
weight. The upper layer of vapor would press on the next 
lower, and this on the next, and so on with accumulating 



-1859] WRITINGS OP JOSEPH HENRY. 263 

weight as we descend ; the aqueous atmosphere surrounding 
the whole earth would thus be found increasing in density 
as we approach toward the liquid surface. If the tempera- 
ture of the earth and of the space around it were 60° F. it will 
be seen by table A, (p. 217,) that the pressure of this aqueous 
atmosphere at the surface of the earth would bo equal to half 
an inch of mercury; if the temperature were 100° it would 
be equal to 2 inches. This pressure however would be 
sufficient to prevent any further evaporation, unless, as 
we have said, an increase of temperature took place. 

In order that such an atmosphere should be in equilibrium 
it would be necessary that the absolute amount of heat in 
equal weights and at different heights should be the same; or 
in other words it should follow the same law as that of a 
gaseous atmosphere. There would however be this great 
difference between the two atmospheres, the one would be 
readily condensed by a diminution of temperature beyond 
a certain point into water, while the other would remain a 
permanently elastic fluid at all temperatures. If therefore 
the space beyond the atmosphere were colder than that 
which would be due to the diminution which would natur- 
ally take place in an aqueous atmosphere, a continual rain 
would be the result, the moisture would be constantly evapo- 
rated from the surface of the earth, and constantly condensed 
by the cold above. Now were it not for the gaseous atmos- 
phere which surrounds the earth and offers a resistance to 
the ascent of the aqueous particles, we think such a condition 
would actually exist. Wo are inclined to this belief from 
the facts which have been stated indicating an exceedingly 
low temperature to the space beyond our atmosphere. 

Be this as it may however, an atmosphere of this kind 
would be exceedingly unstable, and if any portion of tho 
earth's surface were colder than another there would be a 
constant condensation at the coldest parts, and a constant 
evaporation at the warmest to restore the equilibrium. If 
for example the heat of the equatorial regions were 80°, and 
that of the polar regions at zero, the elastic force of tho vapor 
at the former place would be 1 inch, while at tho latter it 



264 WRITINGS OF JOSEPH HENRY. [1855- 

would be but 0*043 of an inch ; hence an equilibrium could 
not exist, and there would be a continued series of currents 
from the equator to the poles, a perpetual condensation of 
vapor into water at the latter, and a constant evaporation 
of liquid into vapor at the former, for the supply of which 
a series of ocean currents would be established. A tendency 
to the same effect must exist in the compound atmosphere 
of air and vapor which actually surrounds our earth, but 
the resistance to the permeation of the vapor is so great that 
a considerable inequality of the elastic force of vapor con- 
tinually exists in different parts of the earth. 

Though there is a constant tendency to a diffusion of 
vapor from the equator to the poles, yet the greatest disturb- 
ance of the equilibrium of our atmosphere results from the 
diminution of temperature as we ascend in the atmosphere, 
and for the establishment of the principle- on which this dis- 
turbance depends, aad the consequences which flow from it, 
we are indebted to the laborious, persevering, and sagacious 
investigations of Mr. James P. Espy. 

From observation it is well known that the air diminishes 
in temperature as we ascend, at the rate of about one degree 
Fahrenheit for each 100 yards or 300 feet. If therefore a 
portion of air be transferred from the surface of the earth to 
a height in the atmospliere, it will be cooled to the temper- 
ature of the stratum of air at which it arrives ; but it is 
proper to observe at the beginning of the explanation that 
this cooling will not be due principally to the coldness of 
the space to which the mass of air has been elevated, but 
chiefly to its own expansion. If the air for example ex- 
pands into double the space by being subjected to lialf the 
pressure, it is evident that the amount of heat which it con- 
tains will bo diffused through twice the amount of space; 
and hence though the absolute quantity of heat remains the 
same, its intensity of action, or its temperature, will dimin- 
ish and the substance will become much colder. This is a 
principle to which we have before alluded, and which will 
be frequently applied hereafter in the explanation of phe- 
nomena. 



-1859] WRITINGS OF JOSEPH HENRY. 265 

If in accordance with the foregoing an upward motion 
takes place from any cause whatever in a mass of air satu- 
rated with vapor, a precipitation must instantly follow. For 
example, if we suppose the moist air to be raised to the 
height of 1,000 yards, and if we further suppose the tem- 
perature at the surface to be 70° the temperature at the 
height of 1,000 yards will be 60° ; and if we inspect table B 
(page 225), at these numbers, we shall find opposite 70° 
7*99 grains of vapor for each cubic foot ; and opposite 60°, 
5*75 grains of vapor for each cubic foot. In this case there- 
fore nearly 2*24 grains of vapor will be converted into water 
and fall as rain. We see from this simple consideration 
that the mere upward motion of a portion of saturated air, 
from whatever cause produced, must give rise to a precipita- 
tion of vapor in the form of water. It may not be in suf- 
ficient quantity to come to the earth in the form of rain, but 
may remain in the air in the intermediate state of a fog or 
a cloud. 

If the air be not saturated entirely with vapor no precipi- 
tation will ensue until it rise to the height at which it be- 
comes by the diminution of temperature fully saturated. 
Suppose for example the air at the surface is 70°, and the 
vapor in it is that due to 65°; then it is plain that it must bo 
reduced in temperature 5° before precipitation commences, 
and this reduction will take place at the height of 500 yards, 
since, as we have just stated, the reduction of temperature is 
one degree for each 100 yards of ascent. And by this simple 
method Mr. Espy has shown that we may, on a given day, 
approximately estimate the height of the base of a cloud by 
merely knowing the dew point at the surface of the earth ; 
for if we find that while the temperature of the air is 70°, 
there is required at the same time to produce a deposi- 
tion of dew on the exterior surface of a tumbler, a reduction 
of temperature of 6° (for example) of the water within, the 
cloud would be 600 yards above the surface of the earth, 
because it will be necessary that the vapor should rise to that 
height in order that the whole mass may bo cooled to the point 
of deposition. The bottom of this cloud will be horizontal, 



266 WRITINGS OF JOSEPH HENRY. [1855- 

bccauso the precipitation begins at a definite temperature 
due to a definite height ; its form will be that of a mushroom, 
bulging out and gradually increasing in altitude; in short, 
will be precisely that form of cloud which is denominated 
cumulus, and which may be seen during a moist warm day 
forming in a still atmosphere, gradually extending upward 
until the precipitation of vapor begins to be so copious that 
the particles of water coalesce and form drops of rain, which 
falling down directly through the base of the cloud, leave 
but a remnant of very attenuated vapor, which is blown 
away and forms, according to Mr. Espy, the cirrus or hair 
clouds. 

We can also readily infer from the same principle that so 
long as a current of air moves horizontally over a plain of 
uniform temperature, no precipitation will take place; but 
if in its course it meets with a mountain, up the acclivity of 
which it will be obliged to ascend and thus come under 
a less pressure and lower temperature, a precipitation must 
ensue. We have in this way a natural explanation of the 
efiFect^of a mountain in causing a cloud and a fall of rain, 
and need not refer the phenomena to the unscientific expla- 
nation of attraction so frequently given ; we say unscientific, 
because the attraction of gravitation at a distance on an atom 
of vapor, is almost infinitely small, and could have no ap- 
preciable effect in drawing the clouds. If we suppose, in ad- 
dition to the preceding case, that the air, after ascending to 
the top of the mountain and forming a cloud by the precip- 
itation of its moisture, descends on the other side to the same 
level, it will arrive at the earth much dryer than it went up. 
If the height of the mountain is not sufiicient to reduce the 
temperature enough to produce a rain, but merely a cloud, 
and if we suppose the current of air to continue its course, 
and to descend to the same level on the other side, it will, 
as it descends, become condensed as it comes under greater 
pressure; the temperature will increase for a like reason to 
that which caused its diminution in the ascent. 

We have in this way an explanation of the paradoxical 
appearance of a strong wind blowing across the top of a 



-1859] WRITINGS OP JOSEPH HENRY. 267 

mountain, while a light cloud, which crowns its summit and 
perhaps hangs over its sides, remains apparently immov- 
able. The truth is that this cloud, which appears station- 
ary, is in reality a succession of clouds constantly forming 
and constantly dissolving. Every portion of air which as- 
cends the .mountain, tends (by its -expansion and cooling) to 
form a new portion of cloud, and in its descent tends (by 
its condensation and increase of temperature) to dissolve a 
similar portion. The cloud is consequently forming on one 
side and dissolving on the other, and in this condition may 
aptly represent the dynamical equilibrium of the human 
body; which, by every expiration of breath is wasting away, 
and by every pulse of the heart is renewed. 

What we have given may be considered as the more ob- 
vious inferences from the first and simplest propositions of 
Mr. Espy 's theory. The phenomena as they occur in nature 
however are more complex, and another effect is produced 
by the upward motion of the air, which very essentially 
modifies the results; we allude to the great amount of heat 
which is evolved during the condensation of vapor into 
water. We have stated that the heat evolved from the com- 
bustion of 20 pounds of dry pine wood is absorbed by a cubic 
foot of water at the ordinary temperature of the air in its 
conversion into vapor, and it is evident that this vapor can- 
not be re-converted into water without giving out to the sur- 
rounding bodies an amount of heat equal to the combustion 
of 20 pounds of dry wood. 

In order to give an idea of the importance of this prin- 
ciple, which is an essential element in the theory, of Mr. 
Espy, it will be necessary to dwell somewhat longer on other 
points before considering more minutely the results to which 
it leads. 

Statical equilibrium of the compound atmospJiere. — Before 
proceeding to discuss the subject further, it will bo necessary 
to consider the question, which appears to be in a very un- 
settled state, as to the effect of vapor in the atmosphere while 
in the act of diffusion. On the one Iiand, the resistance 
which air offers to the diffusion of vapor has been too much 



268 WRITINGS OF JOSEPH HENRT. [1855- 

disregarded, and on the other, we think too much effect has 
been attributed to this cause. It is customary in reducing 
the observations made at European observatories to deduct 
the elastic force of the vapor in the atmosphere at a given 
time from the height of the barometer, and to consider the 
remainder as the pressure of the dry air. This process would 
give a correct estimate of the pressure of the dry air, pro- 
vided the gaseous envelope of the earth were a perfect vacuum 
to the vapor, and the latter were consequently regularly dif- 
fused through the space in accordance with its diminution 
of density due to a diminution of pressure and temperature 
as we ascend; but this we know to be far from the fact. In 
the balloon ascent of Mr. Welsh, on the 21st of October, 1852, 
the tension of vapor at the elevation of 800 feet was observed 
to be greater than at the ground, and at a height of 3,000 
feet it was still greater. In an ascent of the same observer 
on the 17th of the previous August, the tension continued 
to increase until an elevation of 8,400 feet was reached. 

To render this point more clear, we will for a moment con- 
sider the relation of tension and pressure. By the tension of 
vapor, (as has been seen,) we understand the elastic force or 
repulsion of the atoms combined with the action of heat by 
which they tend to enlarge the space in which they are en- 
closed, and to force down the mercurial column in the experi- 
ments by which table A (p. 217,) was constructed. At the tem- 
perature of 60° F. this elastic force is just balanced by a 
column of half an inch of mercury. Let us now consider the 
nature of tension in regard to the atmosphere; for this pur- 
pose let us suppose a piece of paper pasted over the mouth of 
a glass tumbler so as to be air tight. This paper, though of a 
very fragile texture, is not broken in by the superincum- 
bent pressure of a column of air extending to the top of the 
atmosphere and pressing with a force equal to nearly 15 pounds 
on every square inch of the surface of the paper, because it 
is counteracted on the lower surface by an upward pressure 
due to the repulsive action or elastic force, that is to the ten- 
sion of the inclosed air. The weight of the superincumbent 
column on the upper side of the paper is known as the weight 



-1859] WRITINGS OF JOSEPH HENRY. , 269 

or presstire of the atmosphere, while the upward pressure on 
the lower side, due to the repulsion of the atoms, is desig- 
nated indiscriminately by the terms dasticUy, elastic pressure, 
elastie force, and simply the tension of the air. 

The force analogous to the latter (in the case of vapor) is 
more generally known by the name of tension, though it is 
sometimes called elastic pressure. In the foregoing experi- 
ment, if the pressure of the superincumbent air is increased, 
the exterior surface of the paper will assume a concave form, 
the atoms of the inclosed air will be pressed nearer together, 
and their repulsive energy will be increased by the approxi- 
mation of the atoms, and thus a new equilibrium will take 
place. If conversely the column of air above the tumbler is 
diminished in weight, the surface of the paper will assume 
a convex form, because the atoms within the tumbler being 
pressed with less force will separate to a greater distance, and 
the repulsion will be reduced by their separation, until a new 
equilibrium is attained between the pressure without and 
the repulsion within. In this case, variations of the elastic 
force or tension of the air within the tumbler become an 
exact measure of the pressure of the exterior column, pro- 
vided the temperature remains the same; and it is upon 
this principle that the barometer called aneroid is con- 
structed. It consists practically of a flat flask of thin metal, 
filled with air and hermetically sealed by means of solder; 
the motion of the sides of this flask, precisely analogous to 
that of the paper closing the mouth of the tumbler, is com- 
municated by means of lever and wheel work to a hand, 
which indicates the variations of the tension of the inclosed 
air and consequently of the weight of the atmosphere. 

Now if the aqueous vapor formed a separate or entirely 
independent atmosphere around the earth, the variations in 
its pressure would be accurately measured by the variation 
of its tension or elastic pressure at the surface; but since the 
vapor, on account of the resistance of the air with which it 
is entangled, is not uniformly distributed, its tension at 
the surface cannot give a true measure of its whole pressure. 
It is true that as a whole the weight of the atmosphere is in- 



270 WRITINGS OF JOSEPH HENRY. [IBSS- 

creased by the addition of every grain of water which rises 
in the form of vapor from the surface of the earth or ocean, 
but when the evaporation is copious in a limited space, as for 
example, over the surface of a pond of water, or a portion of 
the earth subject to sunshine while the regions around are ob- 
scured by clouds, the elastic force of the vapor tends to dimin- 
ish the specific gravity of the aerial column and to produce a 
fall rather than a rise of the barometer. This is always the 
case while the vapor is in the act of diflPusion; for the resist- 
ance of the atmosphere at the surface of the expanded volume 
of vapor may be considered as an elastic envelope against 
which, as in the case of the India-rubber bag to which we have 
previously alluded, the aqueous atoms press by their repul- 
sion and tend to expand it, and therefore to increase their 
own volume as well as that of the inclosed atmosphere. 

If the vapor ascended into the air without resistance, (as 
in a vacuum,) it would in all cases increase the weight of the 
latter, but on account of the resistance under the conditions 
we have just mentioned, the ascending vapor by its elasticity 
would lift up the atmosphere, tend to lessen its pressure, and 
thus temporarily to expand the air in the space included 
within the surface of the aqueous volume. It is therefore a 
difficult point to ascertain in the explanation of these phe- 
nomena, when we must consider the weight of the atmos- 
phere increased, or when diminished — by the pressure of 
vapor. 

It is evident from the experiments which have been made 
on evaporation under diminution of pressure of air, that the 
resistance to diff*usion spoken of diminishes'in proportion to 
the rarity of the atmosphere; and hence the vapor which 
exists at great elevations -would be in a state of entire diffu- 
sion, and its presence would increase the specific gravity of 
a portion of air through which it is disseminated, instead 
of diminishing it. 

We think erroneous conclusions have frequently been 
arrived at on account of a want of a proper consideration of 
this subject, and from too exclusive an attention to the ex- 
pansive influence of the aqueous vapor in a confined space 



-1859} WRITINGS OP JOSEPH HENRY. 271 

on the one hand, and the increased pressure of the whole 
atmosphere by the addition of vapor on the other. 

It is probable however that in portions of the earth in 
-which the air is constantly saturated at a uniform tempera- 
ture and at which the diffusion is permanently uniform, if 
the elastic force of the vapor is subtracted from the whole 
height of the mercurial column it will give the pressure of 
an atmosphere of dry air. 

On the supposition that the vapor is uniformly distributed 
through the atmosphere, (which will not be far from the 
truth if considered with reference to the principal zones of 
the earth,) we can calculate the whole weight of water con- 
tained. If the water were at the boiling point its elastic 
tension or pressure would be equal to the pressure of the 
atmosphere, and in this case it would support 30 inches of 
mercury, or its equivalent, 407"4 inches of water; and since 
transparent vapor observes the same law of expansion and 
contraction by variations of pressure and temperature that 
dry air does, it is clear that we shall have the following re- 
lation for any other temperature, namely, as 30 inches is to 
the quantity of mercury expressing the elasticity of the air 
at any temperature, so is 407*4 inches of water to the whole 
weight of the aqueous vapor, provided the weight of vapor 
were the same as that of the air. It has however been proved 
by the experiments we have described that vapor is only five- 
eighths of the density of air, and therefore the quantity 
found by the foregoing relation must be reduced in this 
ratio. 

If we assume that the dew-point is on an average G° below 
the temperature of the air, and allowing the temperature of 
the tropical regions to be 82°, we shall have the following 
proportion,— 30 : 0-897 : : 407-4 : 12-181. This last number 
must however be multiplied by |, and this will give us 7013 
inches. From this it will appear that if the atmospheric 
columns at the equator were to discharge their whole watery 
store the moisture precipitated would cover the earth to the 
small depth of 7*613 inches; and from a similar calculation 
we find that if the column of air resting upon the city of 



272 WRITINGS OF JOSEPH HENRY. [1855- 

Washingtou were to precipitate at once all its moisture, 
the quantity of water would be indicated by about 3 inches 
of the gauge. To supply therefore 30 or 40 inches of rain 
in the course of a year it is necessary that the vapor con- 
tained in the atmosphere should be very frequently renewed, 
and that consequently localities which cannot be reached 
by moist winds must be abnormally dry. 

Effects of vapor on the general currents of th^ atmosphere, — 
From what has been previously stated it is evident that the 
atmosphere which surrounds the globe being composed of 
two portions, one of permanent elastic gases, and the other 
of a readily condensable vapor containing a large amount of 
latent heat, it must frequently be in a state of tottering equi- 
librium, liable to be overturned by the slightest extraneous 
forces, and in assuming a more permanent condition to 
give rise to violent commotions, and currents of destructive 
energy. 

It has previously been shown that the equilibrium of a dry 
atmosphere depends upon the fact that each pound from the 
top to the bottom of an aerial column contains approxi- 
mately the same amount of heat. If therefore a portion of 
air be caused to ascend (by mechanical or other means) to a 
greater elevation, it will expand, and its heat being distrib- 
uted through a larger space, its temperature will fall to that 
of the new region to which it has been elevated, and be 
again in equilibrium. If on the other hand a portion of 
air be caused to descend, it will be condensed into a smaller 
space on account of the increased pressure, and its tem- 
perature will be raised to that of the gtratum at which 
it has arrived. But this is not the case with moist air; for if 
by any means it be elevated above a given level, the coldness 
produced by its expansion will, as we have said, condense 
a portion of the vapor into water, and in this process the 
vapor will give out its latent heat to the surrounding air, 
and therefore the column in which this condensation has 
taken place will not be as cold as the surrounding atmos- 
phere; consequently an upward force will still exist, the col- 
umn will rise to a greater height, and a new portion of vapor 



-1859] WRITINGS OF JOSEPH UENRY. 



27a 



will be formed, and so on until all or nearly all the vapor 
will be converted into water. In this way the steam ix)wer, 
which has been accumulated from the heat of the sun, is ex- 
pended in producing commotions of the atmosphere con- 
nected with all the fitful — ^and many of the regular — meteoro- 
logical phenomena of the globe. 

It may be objected to this part of the theory of Mr. Espy 
that the condensation of the vapor in the atmosphere would 
tend to contract it into a smaller space, consequently to 
render it heavier, and thus neutralize the effect of the ex- 
pansion due to the evolution of the latent heat. The effect 
however from Ihis cause is ver}'^ small in comparison to that 
due to the expansion of heat; and this will be plain when we 
consider that the particles of vapor exist in the interstices 
of the particles of air, and in a close vessel tend to in- 
crease the volume only in proportion to their repulsive 
force, which compared with that of the air, is small. For 
example, if a quantity of dry air were inclosed in an India- 
rubber bag, at a temperature of 60°, at the level of the sea, 
it« elastic pressure outward on the sides of the bag would bo 
equal to the weight of 30 inches of mercury, while the elas- 
tic force of vapor would only be equal to half an inch of 
mercury; so that we should have the enlargement of the bag 
expressed by the last term of the following proportion : If 
30 inches of mercury give one foot what will 305 give? 
In this case, which is an extreme one, we sec it would give 
but a little more than 1 per cent., and hence the diminution 
due to extracting the vapor from a quantity of air is very 
small, and far less than the expansion due to the evolution 
of heat. This will be evident from the following calculation 
of the effect produced by the condensation of a pound of 
vapor into water: It is known from direct experiment 
that the condensation of one pound of vapor will raise 970 
pounds of water 1°, or if it were possible to heat water thus high 
it would raise one pound of water 970°; but the capacity of 
air for heat is only one- fourth that of water; therefore the 
condensation of one pound of steam would raise one pound 
of air 3,880°, or 10 pounds of air 388°. The above calcula- 

18-2 



274 WRITINGS OP JOSEPH HENRY. [1855- 

tion is from Danicirs Chemical Philosophy, and is given as 
an illustration of the immense motive power due to the fall of 
a single pound of water in the form of rain. During a single 
rain, in 1857, water fell to the depth of 6 inches in the space 
of 36 hours, and considering merely the amount of ascen- 
sional power evolved by the condensation of the quantity of 
the liquid which fell on the roof of the Smithsonian build- 
ing, it would be equivalent to a thousand horse-power ex- 
erted during one day. 

From these considerations it is evident that the general 
currents of the atmosphere must bo very much modified by 
the action of the vapor, and very different from those de- 
scribed in our previous essays as belonging to dry air. In- 
deed to such an extent are some of the general phenomena 
influenced by this cause, that the motive power of the atmos- 
phere has been referred to other causes than the action of the 
heat of the sun ; but in this case, as in most oth^r exceptions 
to a principle deduced from a wide generalization — like that 
of the action of solar heat on our atmosphere, the facts 
when rightly understood and properly interpreted, serve but 
more firmly to establish the truth. 

We shall now consider more minutely the effect of the 
formation and condensation of vapor in modifying the gen- 
eral circulation of the atmosphere. It has been shown in the 
previous articles, that if the earth were at rest in space, with- 
out revolution on its axis, heated at the equator and grad- 
ually cooled to a minimum point toward the poles, there 
would be a constant circulation of air from the poles, north 
and south, toward the equator. The air would rise in a 
belt encircling the whole earth, and flow backward towards 
the poles above. In this simple circulation, at every place 
on the surface of the earth, in the northern hemisphere for 
example, there would be a perpetual wind from the north 
flowing toward the equator, and above the same place at 
the surface of the aerial ocean there would be a return 
current constantly flowing from the equator toward the 
pole. It is evident however since the meridians converge 
and meet at the pole, that the space between any two be- 



-1859] WRITIKQ3 OF JOSEPH HBNBY. 



276 



comes less aud less as we depart from the equator; hence all 
the air which ascends at the equator could not flow entirely 
to the pole, but the larger portion of it would descend to the 
earth to return again to the equator, along the surface at 
some intermediate point, which would be, on an average, 
about the latitude of 30°, since the space included between 
this and the equator would be nearly equal to the remaining 
surface in each hemisphere. Again as we have seen, the 
simplicity of this system of winds would be interfered with 
hy the rotation of the earth on its axis. On account of this 
rotation, as a general rule, when a current moves from the 
equator, in the northern hemisphere, for example, it would 
gradually curve to the east, and when it moves southward 
in the same hemisphere, it would curve to the west; the 
rapidity of curving in either case would increase aa we ap- 
proach the pole. On account of this curvature and deflec- 
tion east and west of the upper and lower currents, together 
with the disturbance produced by the evolution of the latent 
heat, the simple system we first described will tend to sepa- 
rate, as we shall more fully see hereafter, into three distinct 
systems, which we have represented by A, B, and C, in the 
annexed figure. 
Fig. 5 is a diagram Intended to represent an ideal section 








through a meridian of the northern hemisphere, showing 
the several systems of aerial circulation, commencing on the 
left at £ (the equator), and completing the series on the right 
at P, — the north pole. Fig. 6 is a bird's eye view of the 
globe,' designed to illustrate the prevailing direction of the 



276 



WRITINGS OF JOSEPH HENRY. 



russ 



surface currents, particularly in the nortbem hemisplierf 
By comparing the two figures, it will be seen that the system 
A, B, and C, of Fig. 5, correspond with the three zones o 
arrows id Fig. 6. To supply the air which ascends in tb 
region near the equator, the current on each side, on accouD 

Surface Wiiult of iht OCobe. 




FiQ. 6. 

of the rotation of the earth, takes an oblique directior 
we have seen,) flowing in the northern hemisphere fror 
northeast, and in the southern from the southeast. II 
tinues its westerly motion as it ascends until it read 
culminating point, and tlicn flows backward in an o] 
direction curving as it goes, toward the east. 

The surface currents on either side of the equ 
region, (called the trade winds,) as they pass over th 
constantly imbibe moisture, and deposit but little iu t 
of rain, since there is no ohHacle on the level surfac 
water to produce an upward current and the cor 



-1859] 



WRITINQS OP JOSEPH HENRY. 



277 



diminution of temperature essential to the formation of rain. 
They therefore carry their moisture to the belt of confluence, 
where in the ascent of the air it is precipitated, evolves its 
latent heat, and develops its ascensional power. To render 
the ascent of these currents more plain Fig. 7, may be con- 
sidered a transverse section across the equator at the belt 
of calms. 




The air enters below on either side D G, rises upward in 
the middle space, and spreads out north and south above 
D' (7. As the air ascends it comes under less pressure, ex- 
pands, becomes colder, and on this account condenses a por- 
tion of its vapor, which renders the air warmer and lighter 
than it would be if this evolution of " latent heat " did not 
take place. Hence the ascension continues, and the eleva- 
tion to which the column attains is therefore much greater 
than it would be if the air were void of moisture. The 
condensation of the vapor takes place in the form of a largo 
amount of rain which falls by its superior weight through 
the ascending air, A, B, and deluges the surface immediately 
below, in some places to such an extent that fresh water on 
the surface of the ocean has been found floating on the top 
of the salt water. Indeed more rain falls on the surface 
within this belt than on the whole earth beside. On either 
side of the rain belt a cloud will bo formed by the spreading 
out of the ascending air mixed with vapor, as shown in the 
figure. The falling rain coming from a'high elevation and 



278 



WRITINGS OP JOSEPH HENRY, [1855- 




having consequently a low temperature, will cool the surface 
of the earth below that of the spaces on either side. 

The pressure of the air in the ascending column will be 
less than that on the regions north and south, since a portion 
of its weight is thrown over on erther side. This funda- 
mental principle, which has been strangely mis-understood, 
will be rendered evident 
by the annexed figure 8, in 
which -4, B represents the 
surface of the earth, and a, 
6, and c, d, (the several par- 
allel lines above,) the sur- 
faces of the strata in which ^^Q- 8. 
the air is supposed, for illustration, to be divided. The depth 
of these strata will be throughout the whole column in- 
creased, and the surface of the upper one will be elevated 
above the general surface of the atmosphere. Being un- 
supported, it will tend to flow over on the strata on each 
side; the surface of the next stratum below will also press 
outward with more force than it is pressed inward, and 
will consequently mingle with the air on each side, while the 
heavy air on each side below opposed by lighter air will 
press under the lower stratum and tend to elevate it. Be- 
tween the bottom and the top there will be a neutral surface, 
marked o, which is in equilibrium. 

In the middle space at the bottom of the ascending column 
(Fig. 7), the air will be nearly at rest, subject however to fit- 
ful squalls due to the falling rain, and hence this belt is 
known either as the belt of rains, or of equatorial calms. 
The width across the ascending belt is several hundred 
miles, and though particles of dust or infusoria which enter 
on the south side may occasionally mingle with the air 
which enters at the north and thus be carried northward by 
the upward current, yet the habitual crossing of the two, as 
some have supposed, and the constant transfer of the vapor 
of the northern hemisphere to the southern, and vice versti, 
is in accordance with no established principle of nature, and 
therefore cannot be admitted even as a plausible hypothesis. 



•-1859] . WRITINGS OF JOSEPH HENRY. 279 

On account of the heat evolved, the air in the ascending 
belt receives an additional momentum which carries it con- 
siderably beyond the point of statical equilibrium, and con- 
sequently it descends with a greater velocity, which is further 
accelerated by the cooling to which it is subjected at this 
high altitude by radiating its heat into celestial space. In 
its descent it brings down with it (at about the average lati- 
tude of 30°) the air north of this latitude, giving rise to a 
reverse current, and thus producing two separate systems, 
A and B. (Fig. 5.) The air at the foot of the descending belt 
at the latitude of 30° will press with greater weight than 
that of the average of the atmosphere, hence in this belt at 
the surface of the earth the barometer will stand higher, and 
while the belt of rains is called the middle belt of low bar- 
ometer, the belt of 30° is frequently known as the belt of 
high barometer. At the foot of this belt the air will be 
pressed out toward the north and south ; southward to supply 
trade winds and the air which ascends at the belt of calms, 
and northward to form the current from the southwest, (as 
shown in Fig. 6,) which latter is the prevailing wind of the 
north temperate zone. 

We have thus seen that there would be a tendency to 
separate into the two systems A and B. (Fig. 5.) There 
would also be a tendency in the remaining air to separate at 
the point g^ giving rise to the polar system C Were the air 
within the circle of 60° north latitude entirely isolated from 
the other part of the atmosphere, a circulation would take 
place in this such as is indicated by C, the difference of tem- 
perature between the surface of the earth at the circumfer- 
ence of this circle and the regions in the vicinity of the cold 
pole would be sufficient to produce such a circulation. The 
column of air in the polar region, on account of its low tem- 
perature, would be denser and consequently heavier than 
the surrounding air; it would therefore sink down and 
spread out in every direction from the centre of the column ; 
the air would flow in above to supply the level, while the cur- 
rent below would become heated as it passed southward and 
rise as shown at the point g. In its ascent it would tend to 



280 WRITINGS OP JOSEPH HENRY. [1855- 

carry up with it the surface air of the system B, and thus 
conspire with the downward motion at/ to produce the cir- 
culation shown in system B, 

The upward current at g, (as in the case of the upward 
current at the equator,) will tend to diminish the pressure of 
the air and produce a low barometer and an abnormal fall 
of rain, which perhaps will be more efiPective in helping on 
tho circulation of the system B tlian the mere mechanical 
effect of the uprising of the current of C. The current 
at the surface of the earth in the system C, as is shown 
in Fig. 6, will curve to the westward on account of the 
increased rotation of the earth, and will therefore be almost 
in direct opposition to the system B. If we attentively con- 
sider the efifect of the rotation of the earth on the system B, 
we shall find that as the current passes along the surface 
to the northeast as indicated in Fig. 6, it will begin to 
ascend when it comes near the parallel of 60°, (retaining 
however its easterly direction,) will gently curve round and 
pass southward as an upward current, and flow toward the 
equator as an upper northwest current, shown in the figure 
by the few longer arrows, indicating a northwest wind. 
The system A is the constant circulation of the trade and 
anti-trade winds. The system C depends upon a similar 
cause as we have seen, and is for a similar reason permanent 
in its character. Though but comparatively few observa- 
tions have been made in the polar regions, the character of 
this system does not rest upon more inference from the gen- 
eral principles we have given, but is conclusively established 
by the immediate results of reliable data. Professor J. H. 
CoflBn, in his valuable memoir on "The Winds of the 
Globe," published by the Smithsonian Institution, inferred 
the existence of this system independently of theoretical 
conclusions. From the reduction of all the observations 
he was able to obtain, he conclusively proved that the 
resultant wind from the pole is from a northeasterly 
direction; and the same result is established by the discus- 
sion of the interesting series of observations made during the 
last expedition of Dr. Kane. Tliesc observations, which 



-1859] WRITINGS OP JOSEPH HENRY. 281 

have been tabulated for the Smithsonian Institution, under 
the direction of Professor Bache, by Mr. Schott, of Washing- 
ton, give the same direction to the northern current at the 
surface of the earth within the polar circle. 

That the prevailing motion of the system B is in the direc- 
tion exhibited by the arrows, is abundantly shown by the 
fact of the prevalency of the southwest wind, particularly in 
the summer, over the whole of the temperate zone; and that 
this upper current of the same system is southward and 
eastward, or in other words from the northwest, is attested 
by aeronautic observations in this country, and in Europe. 
The celebrated American aeronaut, Mr. John Wise, (from 
the experience of upward of two hundred balloon ascen- 
sions,) has stated to the writer, that while the current at 
the surface of the earth is from the southwest, at a variable 
elevation of two miles or less, the wind becomes nearly 
due west, and at a still greater elevation it blows from the 
northwest. The direction of the intermediate stratum is 
probably due to the resultant action of the two, and this 
would naturally result from the almost constant action of 
ascending currents, passing with every fall of rain from the 
lower to the upper. A similar testimony is given for West- 
ern Europe by the aeronautic experience of Messrs. Green 
and Mason. According to this, though the prevailing wind 
at the surface is from the southwest, at an elevation of 10,000 
feet the current is invariably from some point north of west. 
Moreover, observations on the direction of the ashes of vol- 
canoes prove the same direction of the upper current. In 
the summer of 1783 the smoke of an eruption of a volcano 
in Iceland was diffused over England, Germany, and Italy. 
From another eruption of a volcano in the same island, in 
1841, the ashes were carried by a northwest upper current 
and deposited on the decks of vessels in the Irish Channel. 

Though the prevailing direction of the currents of the 
system is given in J?, (in Fig. 5,) yet the stability of this 
system is by no means equal to that of Ay or even that 
of (7, since in some cases its direction is apparently entirely 
reversed. The northwest upper current, mingling perhaps 



282 WKITINQS OF JOSEPH HENRY. [1855- 

with the polar current, descends to the surface of the earth, 
(particularly along the continent of North America,) and 
probably gives rise to the phenomena known by the name 
of •** Northers" and possibly also to the more violent north- 
east storms of the coast. While the reversal of this system 
takes place in one part of the earth, the more habitual 
motion may be continued in another, and in this way a 
mild winter in America, produced by a prevalence of south- 
westerly wind, may be accompanied with a severe winter, 
produced by northwesterly winds in some part of Asia, or 
Eastern Europe. 

The belts and systems we have described are not station- 
ary, but move north and south in diflFerent periods of the 
year with the varying declination of the sun. For exam- 
ple, the belt of rains is constantly almost directly under 
the sun, and moves north and south with the changing 
declination of that luminary, and thus divides the year in 
the tropical regions into two rainy and two dry seasons. The 
rain is produced (as has been abundantly shown) by the con- 
densation of the vapor carried up by the ascending current of 
air; the dryness on each side of this belt is the result of the 
descent of the air which has been thrown out above, princi- 
pally deprived of its vapor and increased in temperature both 
by the heat due to condensation and to that absorbed before 
it is tlirown outward from the precipitated vapor. In the 
summer season, when the sun is on the northern side of the 
equator, the trade-wind system extends up on the ocean 
sometimes as high as 40° N. latitude. A similar movement 
takes place, but to a less extent, in the system of the tem- 
perate zone. From this movement it is evident that there 
is not only a variation of heat, but also of moisture and 
precipitation at different seasons of the year. 

It is also necessary to mention that the belt of high barom- 
eter is interrupted across the continent of North America, 
and probably never passes farther north than the portion of 
the United States bordering on the Gulf. But on this point 
we cannot speak positively without more data and further 
investigation. It is certain however that on the Pacific side, 



-1859] WRITINGS OP JOSEPH HENRY. 283 

the belt of high barometer, (or that from which the air flows 
out oa each side north and south,) in summer extends beyond 
the latitude of 40°, and thereby produces a wind from the 
north in this season of the year, while in winter it is found 
below Southern California, and thus gives rise along the 
coast and parallel mountains of the interior to a wind in the 
opposite direction, namely, from a southern point of the 
compass. 

This is a sufficient explanation of the rain which falls at 
that season, since the currents from the south are laden with 
moisture which they deposit in their ascent along the slopes 
of the mountains towards the north. 

On the drawing exhibiting the surface currents, (Fig. 6, 
p. 276,) the point P representing the geometrical pole, is not 
the centre of divergence of the aerial currents which settle 
dowi> in this region. The latter centre is that of the cold 
pole, which probably on account of the unequal distribution 
of land and the currents of the ocean, does not coincide with 
the former. 

Climate of the United Slates. 

An application of the general principles we have given 
will enable us readily to comprehend the peculiarities of the 
climate of the United States, and to see how it must differ 
from that of other portions of the globe. 

In order however to properly make this application, we 
must briefly recall what has been said in previous papers* on 
the circulation of the waters of the ocean, since they have a 
powerful influence in the distribution of heat and the modi- 
fication of diflerent climates of the earth. For the more 
definite comprehension of this, we have prepared a sketcli of 
the western hemisphere, shown in Fig. 9, on which the direr, 
tion of the principal currents of the northern oceans arc 
denoted by arrows, and in explanation of these, we shall 
briefly recapitulate the general theory of the cause and mo- 
tion of these currents. 

If the equatorial regions of the earth were entirely covered 

[See ante J pp. 59-02.] 



284 WRITINGS OP JOSEPH HKNBT. [USS- 

with water, the tradc-win(Js blowing on each side and acting 
on the water would produce a current toward the west, eo- 
circling the whole globe. But since the region of the equator 
is crossed by continents, the continuous current we have 

Oetan CarrenU of the WeaUm Hemitphtre. 




spoken of is broken up and deflected right and left into ex- 
tended circuits; the water blown from the coast of Africa 
along the region of the equator westward is divided into two 
currents, as represented in Fig. 9, one directed northward, 
and the other southward, by the projecting part of South 
America. The northern branch, as shown by the arrows, 
passes through the Gulf of Mexico, and impelled by the 
action of the surface wind and the rotation of the earth, 
makes a complete circuit, returning into itself along the 
coast of Africa, leaving in the centre a large area of stag- 
nant water covered with weeds, and known by the name of 
tlie Sargasso Sea. The entire course of the waters in this 



-1859] WRITINGS OF JOSEPH HENRY. 285 

extended circuit is completed in about three years. In the 
Atlantic Ocean a branch is sent oflf from this circuit, which 
passes northward, impinges on the western coast of Europe, 
and probably skirts the whole circuit of the polar basin, from 
which it passes out on the west side at Behring's Straits. ' 

Two similar systems of currents exist in the Pacific Ocean; 
that in the northern hemisphere passing from Central 
America along the equator to the continent of Asia, is 
deflected northward along the coasts of China and Japan, 
and returns to the equator along the western coast of North 
America. 

Besides these great circuits from the equator, cold currents 
descend from the polar basin. One of these is represented 
by the arrows with double barbs between the Gulf Stream 
and the eastern coast of the United States; and a similar 
one descends along the coast of China between it and the 
Gulf Stream of that region. These are in part derived from . 
the water which is discharged into the polar basin from the 
several rivers of the north, and probably in part due to a 
return portion of the equatorial currents. They skirt the 
eastern shores of the continents, because currents from the 
north (on account of the rotation of the earth) tend to move 
westward, while those from the south tend to move eastward. 

The effect which these great currents of the ocean, (evi- 
dently the natural results of the system of winds which we 
have described,) produce on the climate of the United States, 
compared with that of Europe, can readily bo appreciated. 
The elevated temperature of the water in the Gulf of Mex- 
ico, (higher than that of the water in almost any other 
part of the globe,) is retained by the Gulf Stream until it 
reaches the shores of the polar basin. The southwest winds 
which accompany and blow over the Gulf Stream share 
its temperature, and impart their warmth and moisture to 
Western Europe, giving it a climate far more genial than 
would be due to the latitude. The southwest and west- 
erly winds which prevail over the surface of the United 
States serve to bear the heat of the Gulf Stream from our 
coast, and even when an easterly wind is produced by local 



286 WRITINGS OF JOSEPH HENRY. [1855- 

causes, which would bring the warm air of this stream to 
our shores, it is cooled by crossing the cold current we have 
mentioned, which reduces its temperature to the dew-point, 
and produces the peculiar chilly effect so familiar to the 
inhabitants of the Eastern States during the prevalence of a 
northeast storm : while on the Pacific coast the west winds 
from the ocean cross the comparatively cool current from 
the north and impart their mild and uniform temperature 
to the western slope of the Coast Range of mountains, giving 
rise to the remarkable fact of the summer temperature being 
the same for hundreds of miles in a north and south direc- 
tion. 

Were the whole of North America — from the Atlantic to 
the Pacific — a continuous plain, or were the surface diversi- 
fied merely by eminences of comparatively small elevation, 
the moisture from the Pacific would be carried into the in- 
terior, and a much greater degree of fertility in the western 
portion of the Valley of the Mississippi would exist. In 
the actual condition of the continent however, the westerly 
wind which passes over the great mountain system extend- 
ing from north to south along the western portion of the 
continent, deposits its moisture principally on the western 
slope of the Coast Range, and gives fertility and a mild 
climate to California, Oregon, Washington, and particularly 
to the regions farther north. The amount of rain which 
falls at Sitka, Russian America, amounts in some years to 
60 inches. The remaining moisture which this westerly 
wind may contain is precipitated on the western slopes of 
the high ridges farther east, and when the current has 
passed over the whole Rocky Mountain system, it is almost 
entirely dessicated, and leaves the elevated plains east of the 
Rocky Mountains an arid region, so deficient in moisture as 
to be unfit for cultivation, unless by the aid of irrigation, 
with the exception of occasional oases, and along the borders 
of streams. 

We have seen that two great systems of wind prevail over 
the United States, the upper from the northwest and the 
lower from the southwest. The latter carries the moisture 



-1859] WRITINGS OF JOSEPH IIKNUY. 287 

from the Gulf of Mexico and the Caribbean Sea over the 
whole of the Eastern States of the Union and the eastern part 
of the Valley of the Mississippi, and is therefore the princi- 
pal fertilizing wind of the interior of the continent. Were 
the earth at rest this wind would flow directly northward, 
and would diffuse its vapor over the whole interior of the 
country to the base of the Rocky Mountains; but on account 
of the rotation of the earth it is thrown eastward, and bears 
its moisture in a northeasterly direction, leaving a large 
space, under the lee of the Rocky Mountains, (so to speak,) 
greatly deficient in this element of vegetable production. 

These winds are shown on the accompanying map of the 
United States, which is copied in its principal features from a 
largo map compiled by the Smithsonian Institution. In so 
small a sketch it is impossible to be accurate in the minute 
divisions; though it will serve to exhibit at a glance the rela- 
tive proportions of the principal meteorological regions of 
the country. The northwest winds (those of the upper strata) 
are denoted by the heavier arrows with a circle on the end, and 
the lower ones — the surface or fertilizing winds — b}'^ the finer 
arrows. The dark portion of the map indicates the naturally 
woody regions of the country, well supplied as a whole with 
moisture from the fertilizing winds: the lighter shaded parts 
indicate rich arable prairie, along the streams of which, 
(where there is a local supply of vapor,) wood is found ; but 
these districts as a whole have much less moisture than the 
naturally woody portions. The unshaded or white part of 
the map, within the boundary of the United States, indicates 
the regions so deficient in moisture that no dependence can 
be placed upon them for the purpose of agriculture. In 
some parts of them, where moisture is found, crops may be 
produced, but as a whole they are of little value in the way 
of affording the necessaries of human existence, and hence 
are incapable of sustaining other than a very sparse popu- 
lation. Portions of this unshaded part, on account of the 
nature of the soil, are barren and almost destitute of vege- 
tation ; while other parts, when occasionally watered by a 
fitful shower, yield patches of grass to which the buffalo by 



WniTIHQ3 OP J(»EPH HEHBT. [1895- 




f 



-1859] WHITINGS OF JOSEPH HENRY. 289 

'his instinct is directed, but even these in the course of a 
few weeks are almost reduced to a powder by the drying in- 
fluence of the unscreened rays of a powerful sun. What 
moisture rises from the evaporation of the rain which maj^ 
fall on the regions indicated by the unshaded part of the 
map is constantly carried eastward instead of being precipi- 
tated again on the place whence it rose. 

The direction of the several ridges of the Alleghany 
Mountains is parallel to that of the fertilizing wind, and 
bence these do not materially interrupt the southwestern cur- 
rents, and are consequently sufficiently supplied with moist- 
ure, except in the more elevated valleys which are inclosed by 
a ridge at their southern extremities. 

From the fact, abundantly pfoved by observation, that 
the vapor of the Pacific Ocean does not pass over the ele- 
vated crests of the Rocky Mountain system, it must be evi- 
dent that the idea that the supply of the interior of the North 
American continent comes from the Southern Pacific by 
ascending to the cold regions of the top of the belt of rains 
is entirely untenable. The source from which the moisture 
of the interior is derived is i)rincipally the Gulf of Mexico. 
We shall endeavor to give in a subsetiuent Report an ac- 
count of the climate of the several meteorological districts 
into which the United States may be divided; the remain- 
ing space allotted to this article will be devoted to a brief 
exposition of the storms of the Continent. 

Storms of North America. — The two groat systems of winds 
to which we have so frequently alluded as existing over the 
United Stiites, present their meteorology in a simple form 
and on a very extended scale, while the general features of 
the phenomena of American storms are readily explicable 
on the principles of the theory propounded by Professor 
Espy. And first we may remark that on account of the 
height of the Rocky Mountain system, the storms or other 
commotions of the atmosphere which take place on its 
western side, are seldom if ever communicated to the air on 
the eastern; and this is a natural consequence of the prin- 
ciple which refers these commotions to the evolution of the 

19-2 



290 WRITINGS OF JOSEPH HENRY. [1855- 

latent heat from portions of air charged with moisture. Ac- 
cording to this view, an intervening region ahnost entirely 
without moisture will of necessity tend to intercept the pro- 
gress of a storm, though it is not impossible that the draw- 
ing in of air on one side of a mountain of limited extent may 
cause a current across the mountain to supply the (Jefi- 
ciency. 

We think all the phenomena of the storms of the interior 
of this continent may be referred to disturbances in the equi- 
librium in the upper and lower strata of air. In the first 
place, all the disturbances of the atmosphere, however they 
may be produced, tend to move eastward over the United 
States, because this is the resultant motion of the great mass 
of current passing over the surface of this region. That the 
storms from the interior tend to move nearly east, with a 
velocity of from 20 to 30 miles an hour, is abundantly 
proved by the observations collected at the Smithsonian 
Institution, and the fact is interestingly and practically 
exhibited by means of the daily despatches gratuitously 
furnished tliis Institution by the Morse line of telegraph. 
These despatches are received every morning from the 
greater portion of the country east of the Mississippi River 
and to render the information available in the way of pre- 
dicting probable changes of the weather during the day or 
the following evening, a large map, containing merely the 
names of the places of observation, is attached to a wooden 
surface, into which, at each place, a projecting iron pin is 
driven. Small cards (previously provided) of about an inch 
in diameter, of different colors, to indicate rain, snow, clear- 
ness,and cloudiness, are attached to the map at the respective 
places of observation by means of the iron pins, and changed 
daily to correspond with the telegraphic despatches, so that an 
observer, at a glance, may see the condition of the weather at 
any portion of the country before mentioned. During the 
autumn, winter, and spring, if in the morning the visitor to 
the Institution observes a black patch indicating rain at Cin- 
cinnati, he may conclude that, in about twelve hours after- 
ward, the same storm will reach Washington. Indeed so 



-18591 WRITINGS OP JOSEPH HENRY. 291 

uniformly has this been the case during tlie last year, that 
we have been enabled to decide whether it would be proper 
to advertise during the day the lecture to be given in the 
evening. 

In summer it frequently happens that thunder storms 
commence their course at points intermediate between Cincin- 
nati and Washington, and therefore it will not always fol- 
low that a clear sky in the morning at the former place will 
indicate a clear evening at the latter. But wherever the 
thunder storm commences it always moves eastward, or 
rather eastward inclining to the north, a direction which 
indicates that the direction of these circumscribed storms is 
principally governed by the motion of the lower stratum of 
air. 

The extent of the interior storms, north and south, is ex- 
ceedingly variable. In some cases a storm of not more than 
a hundred miles in width travels eastward along the lakes ; 
and again at another time a storm of a similar width may 
commence at the south and move along the shore of the 
Gulf of Mexico. Again at other times the commotion ap- 
pears to extend from some northern point in the British pos- 
sessions, down to the Gulf of Mexico, and even farther south, 
and to move eastward, side foremost. In this motion the 
southern part of the storm first reaches the Atlantic Ocean, 
in the southeastern part of Georgia, and since the general 
trend of the coast is to the northeast, it is evident that the 
storm will appear to move from soutli to north along the 
coast, while in reality the whole system of disturbance is 
moving eastward, and will finally leave the continent at New- 
foundland. 

Another system of interior disturbances — which commenc- 
ing apparently at the south and confined principally to the 
eastern coast tends to draw in the air from the Gulf Stream 
along the surface, to be carried outward again by the upper 
current, — ogives rise to our northeast storms. These are how- 
ever in a -great degree intercepted by the Alleghany Moun- 
tains, and do not extend very far into the interior. Accord- 
ing to a suggestion of Dr. Hare, these storms are due to a 



292 WRITINGS OP JOSEPH HENRY. [1855- 

heating and rarefaction of the air in the Gulf of Mexico, as 
probably are also the "northers" which descend from the 
western plains. 

Still another system of storms, originating in the Caribbean 
Sea and following the general direction of the Gulf Stream, 
sometimes sweep over the peninsula of Florida, and over- 
lap somewhat upon the eastern coast of the United States. 
These are the great hurricanes, — (or cyclones as they are 
sometimes called,) the character and nature of which have 
given rise to so much discussion. 

During the warm months of summer almost every part 
of the United States is occasionally visited with very violent 
though exceedingly circumscribed commotions of the atmos- 
phere known, as tornadoes or water spouts. These generally 
move in nearly the same direction, — toward the northeast, 
except perhaps on the borders of the Gulf of Mexico, leav- 
ing their narrow path, sometimes only a few rods wide, 
marked with the evidence of energetic action of a most de- 
structive intensity. The question naturally arises, is it pos- 
sible in the present state of science to give a rational explana- 
tion of the various commotions (apparently fitful and complex 
•and without an adequate cause) manifested in the light and 
invisible aerial covering of our globe? Can the question be 
answered? How is it possible that the soft and balmy air, 
which offers scarcely the least resistance to the motion of a 
lady's fan, can yet exert a power sufficient to level with the 
ground the largest trees of the forest in a single minute, to 
the number of 7,000 in the space of a square mile, and this 
devastating energy continue, as it has been known to do, for 
a distance of many miles? 

The phenomena of these violent circumscribed storms, 
which appear peculiarly marked in America, have been inves- 
tigated with much careful and laborious research by Frank- 
lin, Bache, Loomis, Olmsted, Hare, Redfield, Espy,and others. 
We owe to the lamented Professor Mitchell, of North Caro- 
lina, valuable suggestions in re;2;ard to the motions of the 
air in storms of this character. Professor Bache was the 
first to make an actual survey of the track of a tornado, and 



-1859] WRITINGS OP JOSEPH HENRY. 293 

to protract on a chart the relative position and direction of 
the prostrated trees and the lines described by bodies which 
had been moved by the force of the wind. Mr. Chappel- 
smith, of New Harmony, Indiana, has furnished the Smith- 
sonian Institution with an account of a tornado and a map 
of its path, on which are delineated, from actual survey, the 
position and direction of several thousand trees. Professor 
Loomis has also minutely described the effects of a number 
of tornadoes, and has besides investigated with much care 
and extended research the phenomena of several large storms- 
He was the first to adopt the system of preparing a series of 
maps illustrating the phases of the storm at different periods. 

The laborious observations of the lamented Mr. Redfield, 
particularly in regard to the hurricanes of the Atlantic Ocean, 
have intimately, connected his name with the history of 
meteorology, while the theoretical expositions which have so 
long occupied the attention of Mr. Espy have done admirable 
service to the cause of the same branch of knowledge. 

The controversial papers of Dr. Hare, bearing evidence of 
his great logical powers, served to give precision to the views 
of those engaged in these investigations, and thus to elimi- 
nate error as well as to advance the truth. In speaking of 
those who have given interesting expositions of the general 
facts of the meteorology of North America, we ought not to 
omit mentioning Mr. Robert Russell, of Scotland, who visited 
this country a few years ago, and who has since published 
a work on the agricultural resources of the United States 
and its meteorology, which is alike characterized by accu- 
racy and sagacity of observation as well as by candor and 
justness of opinion. 

The facts which have been gathered from the researches 
of those we have mentioned, as well as from other sources, 
ought to be sufficient to furnish an induction of the prin- 
ciples on which these phenomena depend; and although no 
theory at a given time in the history of a progressive science 
can be considered as perfect, yet we believe the general prin- 
ciples on which the disturbances we have mentioned depend 
have'been successfully developed by Mr. Espy ; and though 



294 WRITINGS OF JOSEPH HENBY. [1855- 

in subordinate particulars modifications will be required, 
yet we think the general propositions of his theory will stand 
the t^t of time. 

As a general rule previous to the commencement of an 
extended storm (during winter), the surface current is from 
the southwest or some southerly direction, the temperature 
rises and the pressure of the air diminishes as indicated by 
the fall of the barometer. This state may continue for sev- 
eral days, and we think it is produced by the southerly cur- 
rent increasing in quantity, in velocity, and depth, thereby 
rendering the stratum of air next to the surface of the earth 
abnormally warm and moist, and consequently lighter, while 
the upper current remaining the same, the atmosphere above 
the surface of the earth gradually assumes a state of tottering 
equilibrium. This condition, according to. Mr. Espy, is not 
brought about by the gradual diminution of the density of 
the lower stratum but by the increased density of the upper 
strata, due to the radiation into space of the latent heat 
which had been evolved during a previous storm. We think 
however that both causes are operative. This instability or 
tottering equilibrium will firet take place at the far west, on 
the western plains east of the Rocky Mountains, since (as we 
have before said) the commotions on the western side can be 
but slowly propagated across the high mountain system. A 
storm then consists of the ascent of the lower current into 
the upper and the gradual transfer of the commotion of the 
air eastward. To take the simplest case, let us suppose the 
storm to be of circumscribed character, like that of a water 
spout or thunder storm. In this case after the unstable 
equilibrium has been produced, the slightest disturbance, 
such as the passage of the lower current over a slight eleva- 
tion or over ground more highly heated than the adjoining 
will tend to establish an upward current. The light, warm 
and moist air below will be buoyed up with great rapidity 
and as it ascends will come under less pressure and will ex- 
pand into a larger bulk. If it were perfectly dry it would 
again be in equilibrium, its bulk would be increased, its 
density would be diminished to that of the air to which it 



-1859] WRITINGS OP JOSEPH HENRY. 295 

had ascended, and its temperature would be the same as that 
of the surrounding stratum. But since it contains moisture 
and in expanding becomes colder, a portion of the vapor will 
be condensed, and in this condensation will give out its latent 
heat. Hence the air of the column will be warmer than 
that of the surrounding atmosphere; it will consequently rise 
to a greater height, again expand, again become colder; 
another portion of vapor will be condensed, and another 
amount of latent heat evolved, and thus the air will rush 
up with an accelerated velocity, and probably gather mo- 
mentum suflScient to carry it to a height greater than that 
due to its buoyancy alone. The condensed vapor will fall in 
rain through the base of the cloud, the air on either side of 
the storm will be forced out from the uprising column into 
the surrounding air, and while the pressure at the base of 
the column will be diminished, that on each side will be in- 
creased, hence the barometer will be frequently found to rise 
slightly before the approach of a storm and to sink rapidly 
as the centre of the uprising column approaches the place of 
observation. 

A series of observations has been made at the Smithsonian 
Institution to determine the variations of the barometer 
during the passage of thunder storms, and in every case in 
which observations of this kind have been obtained, a sudden 
fall has been observed in the barometer, and at the moment 
of the descent of the rain a slight elevation, followed again 
by a depression and then a rise, until the normal pressure 
of the day, or perhaps a little greater, has been obta'ined. 
The intermediate rise taking place at the moment of the fall 
of the rain may be properly attributed to the momentum of 
the drops as a sufficient cause. 

Fig. 10 is intended to illustrate the conditions and phenom- 
ena of a commotion of this kind. The dotted space, c d, at the 
bottom represents the lighter atmosphere, consisting of the 
warm southwest current sur-charged with moisture; above 
this the parallel horizontal lines, a 6, and the arrows, indicate 
the direction and position of the upper western current. The 
ascending column is represented by the upward turned arrows 



L 



WRITINQS OP JOSEPH BENBY. 




and the shaded portion above exhibits the cloud formed by 
the condensed vapor which is thrown outward on each side. 
The rain falling in the axis of the uprising column by its 
weight forces out the air in the direction of the arrows at 
the foot of the column. 

When the air is saturated with moisture in warm weather, 
and especially when the sensation called closeness is observed, 
the rushing up of the column through a confined space may 
be so violent that drops of water may be carried up beyond 
the point of congelation and be converted into ice, and these 
will he thrown out on each side, exhibiting the phenomenon 
often observed in storms of this character, of two streaks of 
hail along the course of the tornado. In some cases these 
pieces of frozen water will be caught up by the inblowiog 
air below and carried up again, perhaps several times in 
succession, each time receiving new accretions, and thus 
large hail stones will be formed exhibiting a concentric 
structure in which the centre will bo of a light spongy con- 
sistency, and this succeeded by a stratum of transparent ice 
and this again by another stratum of snowy appearance, and 
so on, the outer surface being covered with large projecting 
crystals of solid ice. These facts arc in strict accordance 
with what we might have predicted from the theory we have 



-1859] WRITINGS OF JOSEPH HENRY. 297 

adopted. If several large drops of water come in contact, 
and by their attraction rush into one larger drop, and if 
this be borne up so high that it begins to freeze, crystal- 
lization will commence at the surface, the air in the water 
will be driven inward as the solidification proceeds, and 
when the freezing is completed it will give a spongy appear- 
ance to the nucleus of the hail stone. As the hail stone is 
carried up a second time it will gather in its ascent another 
quantity of water which will again begin to freeze and pro- 
duce the spongy envelope, inclosing the stratum between it 
and the coat of pure ice, surrounded by a stratum of solid 
ice, and so on. The number of concentric envelopes will 
indicate the number of times the hail stones have been 
carried up, and the collision of the stones in their ascent and 
descent will give rise to the peculiar noise which is heard 
during the passage of a storm of this kind. 

The ascent of bodies in the centre of the up-moving column, 
and their being thrown out at the top, is not a mere matter 
of speculative inference, but rests upon direct observation. 
Bodies are seen to be carried up in the middle of the ascend- 
ing column and thrown out as we have described; but above 
all Mr. Wise, the celebrated aeronaut, gives an account of 
what took place on the occasion of his balloon being drawn 
into the ascending column of a thunder storm. The balloon 
was carried up to a great height, thrown out on one side, 
sunk gradually down, was caught again by the in-blowing 
current which was rushing in to supply the column, again 
violently carried up, and again thrown out, and this several 
times in succession. 

We have here, in accordance with the theory of Mr. Espy, 
a true, simple, and suflBcient explanation of the production 
of hail, which takes place in the hottest and most sultry 
weather, when the air is most highly charged with moisture, 
and consequently when it contains the greatest amount of 
latent ascensional power. The vapor which ascends is de- 
rived from the moisture which a short time before existed at 
the surface of the earth, and since the ascending column 
usually carries up with it a quantity of fine dust, gravel, 



i 



298 WRITINGS OF JOSEPH H£NR7. [185S-: 

pieces of leaves, &c., these are found in the nucleos of the 
hail stones. 

In order that a storm of this kind may be attended with 
hail, it is necessary that it be of considerable violence, in 
order that the drops of water may be carried up to a sufficient 
height, and hence, as we have said before, this phenomenon 
occurs usually in the warmest and most sultry weather. 

The writer is enabled to give the foregoing explanation of 
the nucleus and the alternate spongy layers of large hail 
stones from the eflFects he obtained by freezing water in a 
glass bulb. The freezing commenced at the exterior surface, 
to which the axes of the crystals were at right angles. The 
air contained in the water was forced iu before the advancing 
crystallization, and formed at the centre of the globule a 
spongy mass precisely similar to that which formed the 
nucleus of the hail stone. 

When the uprising column assumes the form of a tornado, 
it is more circumscribed, and is we think generally accom- 
panied by a whirling motion. The power of the current 
however is in an upward direction. The gyration is an acci- 
dental circumstance, while the upward motion is an essential 
one; and the whole power of the tornado to produce mechan- 
ical effects is in this direction; hence as it passes along over 
the surface of the earth, the air flows in on every side to 
supply the up-moving column, trees are drawn in by the 
force of the centripetal current, and thrown with their tops 
towards the path of the tornado. The writer had an oppor- 
tunity, on one occasion, of examining with Professor Bache 
the effects of a tornado after it had passed through an orchard; 
The trees were all prostrated in a strip of about four rods in 
width, with their tops inward toward the middle of the path. 
The whirling tends to contract the dimensions of the column, 
and to give it the peculiar appearance of an inverted cone 
descending from the clouds. The air which rushes into the 
revolving cylinder, charged with moisture, is immediately 
expanded, consequently cooled, and its vapor condensed into 
visible clouds, which gives rise to the peculiar appearance of 
the descending trunk. 



rl859] WRITINGS OP JOSEPH HENRY. 299 

The tremendous ascensional power which is exhibited in 
storms of this kind, although almost exceeding belief, is 
nevertheless in accordance with the established dynamical 
principle of the accumulation of momentum in cases of the 
continued action of a constant force. We are all familiar 
with the velocity given to an arrow by a simple propulsion 
of the breath along the interior of a blow-gun. In this case 
the air presses against the end of the arrow, at first with just 
suflBcient force to move it; but the momentum it has thus 
acquired is retained, it receives another pressure from the 
air, retains the effect of this, and so on, until it leaves the 
other end of the tube with tlie accumulated momentum ac- 
quired during its whole passage through the interior of the 
gun. In the same way the air, as it approaches the uprising 
column below, commences its ascent with an amount of mo- 
mentum which is constantly increased by continued pressure 
from behind. The ascensional momentum therefore becomes 
so great as to furnish a ready explanation for all the exhibi- 
tion of mechanical power which is so frequently witnessed 
in storms of this character in our climate. On account of 
the rarefaction of the air in the centre of the storm in cases 
where it has passed directly over head, buildings are instantly 
unroofed, the sides are throw^n outward, as if by the action of 
gunpowder, chests are broken open, and corks forced from 
empty bottles, in which they have been tightly fitted. In 
these cases the outward pressure being in part removed, the 
unbalanced repulsive energy of the atoms of the air within 
the edifice causes the outward explosion. The force of this 
outward tendency will not be surprising when we reflect upon 
the great pressure of the atmosphere in its normal state, 
which is equal to more than 2,000 pounds on every square 
foot of surface, and which frequently and suddenly experi- 
ences a reduction of a twentieth part of at least this amount, 
or in other words, of 100 pounds to the square foot — an un- 
balanced force abundantly sufficient to produce the effects 
we have mentioned. 

Dr. Hare attributed the violent upward motion of the air 
in tornadoes to a peculiar electrical state of the atmosphere 



I 



300 WRITINGS OF JOSEPH HENRY. [1855- 

in which, while the air was highly positive, the earth was 
negative, and the bodies carried up were repelled from the 
earth and attracted by the cloud, as in the case of the dan- 
cing figures between the two plates, one of which is connected 
with the prime conductor of an electrical machine and the 
other with the earth. We think however with Mr. Espy 
that electricity is altogether a collateral result, — ^an e£fect of 
the storm and not its cause; it is probable however that its 
presence tends to modify the appearance and produce phe- 
nomena of a subordinate character. It is well known that 
when a kite to which is attached a metallic string is sent 
up to a considerable height above the earth, the wire be- 
comes highly charged with electricity, even in a clear day 
when not a cloud is visible; this effect is due to what is called 
induction. The positive electricity of the upper atmosphere 
drives the natural electricity of the wire from its top to its 
bottom, hence the upper end of the wire will be negative 
and the lower end positive; a similar effect must be pro- 
duced on the cloud formed by the uprising column and on 
the column itself, the two form a continuous conductor of 
immense height, and hence like the wire must become 
charged at the lower end with positive electricity of great 
intensitj', which will tend to elongate the trunk downwards 
by repulsion, and which will give occasional discharges to 
the earth as the tornado passes over good conducting sub- 
stances. 

The terrific and appalling grandeur of the tornado strikes 
the beholder with astonishment and awe, now pausing fit- 
fully as if to select with malignant caprice the objects of its 
unsparing fury, now descending to the earth, and again 
drawing itself up, with its deep, loud, and sullen roar; its 
mysterious darkness; its apparent self-moving, resistless rev- 
olutions; carrying upwards branches of trees, beams of 
houses, and large objects of every description ; its impetuous 
downward rush to the earth, and then again up to the sky, 
its sublime altitude, sometimes erect and at other times in- 
clined; its reeling.and sweeping movements; all these and 
more to be adequately conceived must be actually witnessed. 



-1859] WRITINGS OF JOSEPH HENRY. 301 

The thunder storm differs from the tornado in its less con- 
centration, and consequently in the less intensity of its vio- 
lence. It occurs usually in the United States in the after 
part of a sultry day, when the air has attained its maximum 
amount of vapor, and has therefore assumed a condition of in- 
stable equilibrium. These storms are usually produced over 
a considerable extent of country on the same day, and occur 
nearly at the same hour for several days in succession, and 
probably serve to restore a more stable equilibrium to the 
air, and thus perform the oflBce of the great winter storms 
which sometimes regularly succeed each other at given inter- 
vals. Their general course is eastward, but they sometimes 
deviate from this direction to a certain extent, apparently on 
account of the attraction of water courses; they partially ex- 
haust, carry up and precipitate the moisture of the atmos- 
phere, but sometimes leave the air immediately afterwards 
in a sultry condition. We hope to be able to give in another 
article an exposition of the electrical phenomena exhibited 
by thunder storms, but we may mention here the fact of the 
almost instantaneous fall of rain after each peal of thunder. 
It has been supposed that the drops of rain in this case were 
produced by the agitation of the discharge of lightning; but 
a little reflection will render it evident that the rain must 
have commenced its rapid descent before the discharge took 
place, since it follows the flash at so short an interval that 
we must suppose that it commenced to fall previous and not 
subsequent to the discharge. It is more probable that the fall 
of rain, on account of offering a conducting medium for the 
electricity, is the cause and not the consequence of the dis- 
charge in question. 

The great interior storms we have mentioned usually com- 
mence at the Far West, even at the base of the Rocky Moun- 
tains, and generally occur in November, December, January, 
February and March. They are sometimes of great extent 
in a north .and south direction. One of these storms, that of 
1836, which was investigated with so much ability by Pro- 
fessor Loomis, reached from the Gulf of Mexico to unknown 
r^ions in the north. They are of varying breadth, some- 



302 WRITINGS OF JOSEPH HENRY. [18SS- 

times several hundred miles across, and the cloudiness pro- 
duced frequently overspreads simultaneously a considerable 
portion of the eastern part of the United States. 

In common with nearly all the commotions of the atmos- 
phere on the North American continent, they move east- 
ward, at the rate sometimes of thirty-five miles an hour. In 
some rare instances the horizontal axis of the storm in a 
north and south direction is nearly a icontinuous straight 
line, and moves side foremost toward the east, in the form of 
an immense wave, or rather undulation. The pressure on 
the middle of this wave, on account of the uprising air, is 
less than the normal pressure of the atmosphere, while on 
either side, and particularly on the east, it is greater. 

This pressure on the front and rear of the storm is due to 
the spreading out above of the air which has been carried 
up in the ascending current, and is greater on the east side 
of the storm on account of the action of the westerly current 
in which the whole commotion is carried forward. The 
approach of the storm is therefore generally indicated by a 
rise of the barometer, which is succeeded by a subsequent fall, 
and also by an increase of temperature due to the radiation 
from above of the latent heat evolved, and also by the in- 
creased pressure of the air forced out above. Sometimes the 
horizontal axis of the storm is curved, and again, which is 
of more frequent occurrence, broken, up into a number of 
separate parts, forming altogether a system of which the sev- 
eral portions slightly vary in direction and velocity in their 
motion to the east. 

These great storms, though of the same general nature as 
the thunder storm, are attended with an entire subversion 
of the upper and lower strata of the atmospheric ocean. 
After one of them has swept over the continent the commo- 
tion is immediately succeeded by a westerly wind, a great 
reduction of temperature, and a great increase in the degree 
of dryness of the air. AVe have endeavored to give an idea 
of the motions of the strata of the atmosphere accompanying 
these changes in Fig. 11, which exhibits an imaginary sec- 
tion of the currents in an east and west direction. 



WRITINGS OF JOSEPH HBNBY. 




Fia. 11. 

Previous to the cominencement of the storm there exists 
over the surface of the United States a lower stratum of air 
moving from southern points of the horizon, and over this 
at an elevation of two or three miles the constant current • 
from the west continues its habitual and un-iiiterrupted 
course. The lower stratum, coming principally from the 
Gulf of Mexico, is abnormally warm, moist, and light, while 
the super-stratum is in its usual condition, and the whole is 
therefore in a state of unstable equilibrium. At the far west 
this lower stratum begins to be invaded by the denser air 
from the polar current, which coming from the northwest 
aud mingling with the upper current, presses under, and 
turning the moist cun-ent upward produces an ascending 
column, or rather wall, which mingling with the upper cur- 
rent is carried rapidly to the east. The upper current is 
continued with varying energy, and by the condensation of 
the vapor from the lower, forms clouds and rain, which are 
carried in advance to the east, as the whole system of dis- 
turbance is borne in the same direction by the ordinary 
eastward flow of the upper current of the aerial ocean. The 
primary lower current is shown in the figure by the stratum 
a; the upper current, whicli has tilled the whole space on 
the west down to the earth, by bb; the portion of the prim- 
ary upper current into which the stratum a has ascended 



304 WRITINGS OF JOSEPH HENRY. [X855- 

and in which its vapor has been condensed into clouds and 
rain is represented by c. 

As the storm advances eastward, it leaves the country be- 
hind it entirely covered with the westerly current, and in 
this way carries before it to the ocean the greater portion of 
the vapor with which the lower stratuno, previous to the 
commencement of the storm, was saturated. The rain which 
falls at any given place is formed of the condensed moisture 
which a few hours previous existed at the surface of the earth 
in the same spot or its vicinity. 

We have represented in Fig. 11 the whole cloudiness 
thrown eastward in advance of the storm, but in some cases, 
with a more energetic upward motion, a part of the ascend- 
ing air will be thrown out to the west above; but this can 
scarcely ever take place to the same extent as on the eastern 
side. After the upward moving column has passed over a 
given place, the wind which was previously from the east, will 
suddenly change to the west, the sky will become clear and 
a great reduction of temperature follow. The whole e£fect 
then is due to the instable equilibrium produced in the air 
by the introduction of moisture and the accompanying 
elevation of temperature, together with the subsequent evo- 
lution of the latent heat. A similar condition of the atmos- 
phere preparatory to the formation of another storm will 
gradually be re-produced. The westerly wind will again be 
buoyed up by the warm air from the south, it will therefore 
disappear at the surface of the earth, at which a calm will at 
first exist, the southerly wind will increase in velocity, the 
thermometer and hygrometer will indicate a higher tem- 
perature and increasing amount of vapor, the barometer will 
fall, and after a given interval another instable equilibrium 
will be produced, to be followed by another subversion of 
the strata of the aerial ocean and the repetition of all the 
previous phenomena. The intervals between two successive 
storms will also depend on the time of radiation into celes- 
tial space of the evolved heat, in order to reduce the upper 
stratum to its normal condition of temperature and density; 
but the time required to produce these effects is frequently 



-1859] WRITINGS OF JOSEPH HENRY. S05 

in winter very nearly the same for several successive periods. 
For example, most persons can remember the successive 
occurrence of a series of storms on Sundays. In one case 
we recollect this to have taken place six times in succession. 
There is nothing in this particular day to induce the occur- 
rence of a storm, but merely it will be more likely to be 
remembered when it happens at this time; and although 
the interval between two storms may not be precisely seven 
days, yet it may differ so little from this that a part of the 
first and sixth Sundays may be included in the cycles of 
disturbance. 

The wind as a general rule tends to flow towards the axis 
of the storm from each side, but at the surface of the earth, 
diversified with hills and valleys, the direction is far from 
being as regular as at first sight might be expected. Besides 
this, since the commotion of the atmosphere is usually 
divided into a number of separate groups — each having a 
separate ascending column or belt to which the in-blowing 
air is directed, — the arrows on the map indicating the direc- 
tion of the winds generally present a very complex system 
of currents. On this account also, the rain does not simul- 
taneously fall along an extended line from east to west but 
in separate places, the position of which is determined 
probably by the greater amount of moisture, and conse- 
quently the more intense action of the ascending current. 
As the storm approaches the eastern part of the United 
States however the in-blowing air to supply the up-moving 
current draws in the air from the ocean, charged with 
moisture; which being constantly supplied, the action may 
continue for several days, and the storm may perhaps be- 
come stationary, giving rise to prolonged easterly currents. 

It would appear however from observations at the Smith- 
sonian Institution, that the northeast storms are produced by 
the rarefication of air on the east side of the Alleghany 
Mountains, being frequently independent of a previous in- 
terior storm from the west. 

A considerable number of storms has been mapped in 
accordance with the plan first adopted by Professor Loorais, 

20-2 



306 WRITINGS OF JOSEPH HENRl^ [1855- 

exhibiting on the successive maps by colors the positions 
and movements of the lines of equal pressure and of equal 
temperature. We have not been able to find however (except 
in very rare cases) the advance of the storm side foremost in 
a continuous line. The conditions presented are similar to 
those we have described, namely a series of centres of com- 
motion advancing eastward. . 

The storms next to be noticed are those spoken of as hur- 
ricanes, or cyclones, the true character or nature of which has 
given rise to much discussion between the advocates of the 
two rival theories, of an entirely horizontal gyratory motion 
of the wind on the one hand, and an in-blowing to a central 
area and upward motion of the air on the other. 

Much of this discussion undoubtedly arose from the want 
of precision in the earlier conceptions of the motions of the 
air when referred to the surface of the earth, as in the case 
of a gyration, and in many cases to the ambiguity of the 
language in which these views were expressed. While Reid 
and Piddington supposed the motion of the wind to be in 
concentric continuous circles, and Mr. Espy at §rst in direct 
radial lines towards the centre, Mr. Redfield finally adopted 
an intermediate view, namely of a spiral inward motion. 
We are entirely convinced from the observations which have 
been collected at the Smithsonian Institution in regard to 
the large interior storms that they are not rotatory, and that 
when the gyrations do take place, (as they must in some 
cases on account of the in-blowing currents from all direc- 
tions not exactly opposing each other,) the gyration is a sec- 
ondary motion, the principal force being exerted in an 
upward direction. We are unable to conceive of any ade- 
quate cause of the great and continued velocity of the air in 
a circle of several hundred miles in diameter except tliat 
which is due to the heat evolved by the condensation of the 
vapor with which this portion of the atmosphere is satu- 
rated. This appears to be the true and sufficient source of 
the great motive power, and to afford (when connected with 
the rotation of the earth) a complete explanation of all the 
phenomena. These storms as we have said commence in 



-1859] WRITINGS OF JOSEPH HENRY. 807 

the Caribbean Sea, and describe a curve on the surface of 
the earth almost precisely the same as that which would be 
exhibited by the projection on a horizontal surface of the 
path described by an atom of air in its ascent at the equator, 
in its passage westward, and in gradually curving round 
toward the east. Mr. Redfield has shown that these curves 
in whatever longitude of the northern hemisphere the hur- 
ricanes have occurred, are of precisely the same character. 

If it be admitted that the motive power of this violent 
commotion of the atmosphere is due to the evolved heat of the 
moisture of the air, it will follow that such storms will be most 
frequent and of greatest intensity in portions of the earth 
where the relative amount of moisture is greatest, and that 
they will therefore be found in the greatest number in the 
heated and moist air directly over the Gulf Stream. The 
atmosphere over this area must be in the highest degree in 
a state of tottering equilibrium, since the air rising from the 
heated surface along the axis of the stream must be much 
more highly charged with moisture than that on either side. 
Observation and theory are here in accord. 

These storms sometimes overlap the eastern coast of the 
United States and produce great destruction of property 
along the seaboard, and frequently a loss of life and shipping 
in the region of the Gulf Stream. 

Hurricanes of the same character are found in the south- 
ern hemisphere, describing similar curves, which turn south 
however from the equator round to the east, in an opposite 
direction to that of the curves described by the hurricanes 
of the northern hemisphere. The space to which we are 
limited in this article precludes a more minute discussion 
of the phenomena which have been observed, and the opin- 
ions which have been adopted, in regard to these storms. 
We may have an opportunity of resuming the subject on 
some other occasion. 

In this paper we have endeavored to give an exposition 
of the general principles of the meteorology of the United 
States, reserving for a future report a more detailed account of 
the climatology of its diflFerent portions. We have especially 



308 WRITINGS OF JOSEPH HENBY. [1855- 

endeavored to exhibit our views of the theory of Professor 
Espy and to show its applicability to the explanation and in 
some cases to the prediction of the great commotions of the 
atmosphere. We think this theory has not received the 
attention from foreign meteorologists which its merits de- 
mand, and this perhaps has arisen from the fact that it has 
not been presented to the public in a form which would 
commend it to the immediate attention of scientists. It has 
been frequently coupled with propositions for the artificial 
and economical production of rain, which — however well 
based on scientific principles — would be too uncertain and too 
expensive to render them of any value in a practical point 
of view : and it must be confessed that the language of Mr. 
Espy in regard to the proofs of the truth of his theory, and 
of its great value as a scientific generalization, has occasion- 
ally been such as to awaken opposition to it rather than to 
secure its approval and final adoption.* 

[* Fifty-six pages of Meteorological Tables following this part are omitted 
in the present re-print.] 



-1859] WRITINGS OP JOSEPH HENRY. 309 



METEOROLOGY IN ITS CONNECTION WITH AGRICULTURE. 

PART V. — ATMOSPHERIC ELECTRICITY. 
(Agricultural Report of Commissioner of Patents, for 1859, pp. 461-524.) 

In this paper we intend to give a sketch of the general 
principles of atmospheric electricity; — a branch of meteor- 
ology which has attracted in all ages more attention, and has 
been regarded with more interest, than perhaps any other. 

The vast accumulation of electricity in the thunder cloud, 
and the energy exhibited in its mechanical, chemical, and 
physical eflFects, have impressed the popular mind with the 
idea of the great eflBciency of this agent in producing at- 
mospheric changes, and have led to views of its character 
not warranted by cautious induction. It is frequently con- 
sidered suflBcient in the explanation of an unusual phenom- 
enon to refer it simply to electricity. References of this kind 
however are by no means satisfactory, since the scientific 
explanation of a phenomenon consists in the logical refer- 
ence of it to a general law; or in clearly exhibiting the steps 
by which it can be deduced from an established principle. 
Electricity is subject to laws as definite and invariable as 
those which govern the mechanical motions of the planetary 
system. In one respect indeed, there is a great similarity 
between them, and it will be seen in the discussion of elec- 
trical phenomena, that these are referable to forces similar 
in action to that of gravitation ; and that the mathematical 
propositions which were demonstrated by Newton in regard 
to the latter, have been applied with admirable precision to 
represent those of the former. 

In giving a general exposition of a subject of this kind, 
two plans may be adopted : either a series of facts may be 
stated, and from these a theory gradually developed by a 
careful induction, or we may begin with the general princi- 
ples or laws which have been discovered, and from these de- 
duce the facts in a series of logical consequences. The first 
method is called induction, the second, deduction ; and they 



310 WRITINGS OP JOSEPH HENRY. [1855- 

are sometimes known by the more scholastic names of 
analysis and synthesis. The first method may perhaps be 
considered the more rigid, and where a systematic treatise 
on a subject is intended, and ample space allowed for its full 
discussion it might be preferred; but where the object is to 
give the greatest amount of information in the shortest time, 
to put the reader in possession of the means through which 
by his own reflection he can deduce from a single principle 
hundreds of phenomena, and declare — ^prior to experiment 
or observation, what will take place under given conditions, 
the latter method will be the proper one to be adopted. 

It is impossible however to state a principle of very gene- 
ral application without employing an hypothesis or an as- 
sumption which though founded on strict analogy may 
possibly not be absolutely true. We adopt such an hypoth- 
esis temporarily, not as expressing an actual entity, but as 
a provisional truth which may be modified or even aban- 
doned when we find it no longer capable of expressing all 
the phenomena. All we assert positively in regard to such 
an hypothesis is that the phenomena to which it relates and 
with which we are acquainted at the time exhibit themselves 
as if it were true. 

When an assumed hypothesis of this kind furnishes an 
exact expression of a large number of phenomena, and 
enables us beforehand to calculate the time and form of their 
occurrence, it is then called a theory. The two terms — hypoth- 
esis and theory — though in a strict scientific sense of very 
different signification, are however often confounded and 
otherwise mis-applied. Theory ^ in common language, is fre- 
quently used in contradistinction to /ad, and sometimes 
employed to express unscientific and indefinite speculations. 
The cause of truth would be subserved if these terms were 
used in a more definite and less general sense; for example, 
if the term speculation were restricted to those products of the 
imagination which may or may not have an existence in 
nature; the term hypothesis to suppositions founded on anal- 
ogy and which serve to give more definite conceptions of 
laws ; while the term theory is reserved for generalizations 



-1859] WRITINGS OP JOSEPH HENRY. 311 

which although presented in the language of hypothesis, 
yet really furnish the exact expression of a large class of facts. 

Hypotheses — Well conceived and properly conditioned 
by strict analogy, not only enable us, as above stated, 
to embrace at one view a wider range of phenomena, but 
also assist us in passing from the known to the unknown. 
When rightly used they are the great instruments of dis- 
covery, giving definite direction as to the experiments or 
observations desirable in a particular investigation, and thus 
marking out the line of research to be pursued in our en- 
deavors to enlarge the bounds of the science of our day. We 
think that the tendency of some minds, instead of being too 
speculative is too positive; and while on the one hand there 
is too much of loose, indefinite, and consequently of useless 
speculation intruded upon science, on the other hand an evil of 
an opposite kind is frequently produced by attempting to ex- 
press scientific generalizations of a complex character with- 
out the aid of proper hypotheses; and to this cause we would 
principally ascribe the looseness of conception which fre- 
quently exists in well-educated minds as to the connection 
and character of physical phenomena. 

In accordance with the foregoing remarks we shall make 
use of a theory to express the well-established principles of 
electrical action, and from this endeavor to deduce such con- 
clusions as are in strict conformity with the observed phe- 
nomena. The intelligent reader who attentively studies this 
theory, and exercises his reasoning faculties in drawing con- 
clusions from it, will be able not only to explain many re- 
markable appearances which would otherwise be entirely 
isolated, but also to anticipate results, and to adopt means 
to prevent unpleasant occurrences or to ward off dangers. 

The theory which we shall adopt is that invented by 
Franklin, and extended and improved by Epinus and Caven- 
dish. It is sometimes called the theory of one fluid, in con- 
tradistinction to the theory of Dufay, of two fluids. The 
two theories however do not differ so much as at first sight 
might be supposed, and when expressed mathematically are 
essentially the same. 



312 WRITINGS OF JOSEPH HBNRT. [1855- 

No part of the writings of Franklin exhibits his sagacity 
and his power of scientific generalization in a more conspic- 
uous light than his theory of electricity; The talent to 
discover isolated facts in any branch of science, although 
possessed by few, is comparatively inferior to that character- 
istic of mind which leads to the invention of an hypothesis 
embracing in a few simple propositions whole classes of com- 
plete phenomena. 

Theory of Electricity, 

According to the theory of Franklin all the facts of ordi- 
nary electricity may be referred to the action of a subtle 
fluid, which perhaps fills all inter-planetary space, and may 
be the medium of light and heat. In order that the phe- 
nomena of electricity may be represented by the mechanical 
actions of this fluid, it is necessary to suppose that it is en- 
dowed with certain properties and relations which may be 
expressed in the following series of postulates : 

1st. The electric fluid (or sethor) consists of atoms so min- 
ute as to exist between the atoms of gross matter. 

2d. The atoms of the fluid repel each other with a force 
varying inversely as the square of the distance; that is, 
when the distances are 1, 2, 3, 4, 5, &c., the forces are 1, J, 

h iV* ^V* &C. 

3d. The atoms of the fluid attract the atoms of ordinary 
matter with a force also varying inversely as the square of 
the distance. 

4th. The atoms of gross matter devoid of electricity tend 
to repel each other also with a force inversely as the square 
of the distance. 

5th. The atoms of the fluid can move freely through cer- 
tain bodies of gross matter, such as metals, water, &c., which 
are hence called conductors, and cannot move, or but very 
imperfectly, through other bodies, such as glass, baked wood, 
dry air, &c., which are called non-conductors. 

6th. When each equal portion ofspace has the same amount 
of electricity, and each body in it has so much of the same 
fluid as to neutralize the attractions and repulsions of the 



-1859] WRITINGS OP JOSEPH HENRY. 313 

matter, there are no indications of electrical action; and 
when the attractions and repulsions are thus neutralized a 
body is said to be in its natural condition. 

7th. The electrical equilibrium may be disturbed by fric- 
tion, chemical action, change of temperature, &c., or in other 
words (by these and other processes) the fluid may be accu- 
mulated in one portion of space, and rendered deficient in 
another, and in this case electrical action is exhibited. 

8th. The phenomena are of two classes, namely statical, 
or those of attraction and repulsion, in which the electricity 
is at rest, and dynamical, or those in which the redundant 
electricity of one portion of space is precipitated into that of 
another in which there is a deficiency. 

9th. When the electrical equilibrium has been disturbed 
and a body contains more than its share of electricity, it is 
said to be positively charged; and when it contains less, it 
is said to be negatively charged or electrified. 

The fourth proposition of this theory was added by Caven- 
dish, in England, and by Epinus, in Germany, and was 
found to be necessary in order to render the several parts of 
the theory (as given by Franklin) logically consistent with 
each other. At first sight it appears to be contrary to the 
general fact of the mutual attraction of all bodies, but it 
must be observed that when gross matter exhibits attraction 
it is in its normal condition, and that since the electrical 
force is infinitely more intense than that of gravitation the 
latter may be a residual phenomenon of the former. 

According to this theory, there are two kinds of matter in 
the universe, — ^setherial or electrical matter, and gross (or as 
it is frequently called by way of distinction,) "ponderable" 
matter. The two however may have the same essence, and 
differ from each other only in the aggregation of the atoms 
of the latter; or what we call gross matter may be (as sug- 
gested by Newton,) but a segregation or kind of crystalliza- 
tion of the cetherial matter in definite masses. Each kind 
of matter is in itself entirely inert, has no power of spon- 
taneous change of place, and is equally subject to the laws of 
force and motion. A mass of ordinary " ponderable " matter, 



314 WRITINGS OP JOSEPH HENRY. T^^^^- 

when oDce at rest, tends to continue at rest until put in motion 
b)^ some extraneous force; so also the electrical fluid, when at 
rest, tends to remain at rest, and only moves in obedience to 
some impulse from without. From this theoretical inference, 
which is in accordance with all observation it is an error to 
suppose that electricity is an ultimate power of nature, being 
in itself the cause of motion. Like the air, it is inert, and 
has no more tendency to spontaneous motion than this or 
any other fluid which may receive and transmit impulses, 
or which may have its equilibrium disturbed, and in the res- 
toration of this equilibrium, give rise to motion and pro- 
duce mechanical effects. 

Perhaps some currency is given to the idea that electricity 
is not subject to the mechanical laws which govem the actions 
of gross matter, because it is called an " imponderable" agent, 
and has thus assigned to it a kind of semi-spiritual char- 
acter. The term " imponderable," though convenient, is not 
properly applied, since it indicates a distinction which may 
possibly not exist. If electricity is in reality a fluid, it might 
exhibit weight, could it be so isolated and condensed as to 
become sensible to our balances. But Whatever may be its 
nature, the phenomena which it exhibits can be referred to 
mechanical laws; and it is in order that such a reference 
may be definitely made, that the hypothesis of a fluid is 
adopted. For a similar reason the phenomena of light and 
radiant heat are referred to the vibrations of the setherial 
medium, and it is in this way that the laws of motion which 
have been deduced from the study of gross matter have been 
so successfully applied to them, and it is only so far as 
the facts of what are called the "imponderable" agents are 
brought under the category of mechanical laws that they take 
the definite form which entitles them to the name of science. 

Theoretical Deductions and lllustraiions. — We do not intend 
to develop from the theory we have presented a complete 
system of electricity, but to give such deductions from it as 
will put the intelligent reader in possession of the principal 
known facts of atmospheric electricity, and particularly those 
which relate to thunder storms. 



-1859] 



WRITINGS OP JOSEPH HENRY. 



315 




In the first place, if the setherial medium in its ordinary 
state of diffusion fills all space, then it must be evident that 
when a body is charged with more than its natural share, 
a portion must be drawn from space around, and hence 
what one body gains other bodies in the vicinity must lose, 
or in other words there must always be as much negative 
excitement as positive. To exhibit this, as well as to illus- 
trate some of the effects of the disturbance of the electrical 
equilibrium, provide two strips of glass an inch in width and 
twelve inches long, and on the end of one of these fasten with 
beeswax or sealing-wax a piece of woollen cloth about an inch 

and a half long; if the glass 
slips are warmed and rubbed 
together, as shown in Figure 
1, and afterwards separated, 
they will exhibit signs of elec- 
tricity. If the strip of glass of 
which the end is naked be 
brought near a pith-ball C, sus- 
pended by a single fibre of non- 
conducting silk, so that the 
electricity which may be com- 
municated to the ball cannot 
escape, the ball will be attracted, 
and immediately afterwards re- 
pelled. If now the end of the 
other glass having the woollen 
cloth on it be brought near to 
the same ball, attraction will 
take place at a considerable dis- 
tance. The one slip of glass will constantly attract, while 
the other will as constantly repel the ball. If however the 
two glasses be placed in contact as they were when first 
rubbedj and thus presented to the ball, neither attraction 
nor repulsion will be exhibited. 

These results are in strict accordance with the theorv we 
have adopted. By rubbing the glass and woollen cloth 
against each other the electrical equilibrium is disturbed — 




dc 



Pig. 1. 



316 WRITINGS OP JOSEPH HENRY. [1855- 

a portion of the natural electricity of the cloth is transferred 
to the glass ; the latter receives a positive charge of elec- 
tricity, while the woollen cloth loses a portion of its natural 
share of the fluid, and assumes the negative state; and since 
the slips of glass, as well as the surrounding air, are non- 
conductors, the redundancy of the one cannot escape, nor 
the deficiency of the other be supplied, and therefore the 
charged condition of each will continue for a considerable 
time, particularly if the air be perfectly dry. 

When the glass plate is made to touch the ball a portion 
of electricity accumulated on the surface of the former is 
transferred to the latter, which has then more tlian its natu- 
ral share; and since atoms of free electricity repel each 
other, the ball will apparently be repelled from the glass; 
and also because there is an attraction between free elec- 
tricity and un-saturated matter, the cloth which is in this 
condition will attract the same ball. When the two slips 
of glass are brought together and presented as a whole the 
attractions and repulsions may still be considered as exist- 
ing, but since they are equal and opposed they entirely 
neutralize each other, and no external effect is perceptible. 

The neutralization of the two opposite forces in this ex- 
periment affords an illustration of the condition of a body 
in its natural state. Although it contains a large amount 
of the fluid no action is produced on other bodies in their 
natural condition because the attractions and repulsions just 
balance each other. 

For exhibiting the most important statical phenomena of 
electricity, and for verifying the deductions from the theory, 
we may employ a solid glass rod of about fifteen inches in 
length, and a rod of sealing-wax or of gum shellac of the 
same length. If these be well dried, held by one end and 
rubbed with a piece of woollen cloth at the other, electrical 
excitement will be produced. Instead of a solid glass rod 
a tube may be employed, provided the interior be perfectly 
dry, and well corked to prevent the access of moisture. If 
the end of the tube or rod be rubbed, and afterwards brought 
into contact with a small ball of pith, or of any light con- 



-1859] WRITINGS OF JOSEPH HEKEY. 317 

ducting matter, suspended hj a silk thread, the excitement 
will be communicated to the ball, and if the communication 
be from the glass rod the electricity ^ill be that denomi- 
nated positive ; if from the rod of sealing-wax or shellac, 
it will be what is called negative. Since the phenomena 
exhibited by balls charged negatively and positively are 
very nearly the same, it is not of much consequence which 
we call the positive or which the negative, provided we al- 
ways apply the same name to the same kind of excitement. 
In the early discovery of the two kinds of electrical excite- 
ment, that which was produced by rubbing glass with a 
woollen cloth was called vitreous, and that from the friction 
of the same substance on sealing-wax or gum shellac was de- 
nominated resinous, and these terms are still retained, par- 
ticularly in foreign works on the subject. 

The simplest instrument for exhibiting the attraction and 
repulsion of electrified bodies, and determining the intensity 
and character of the excitement, is the gold leaf electrometer, 
or electroscope, which any person with a little patience and 
some mechanical skill may construct for himself Different 
forms of this instrument are exhibited in Figures 2, 3, and 8. 
A brass wire, surmounted by a 
ball of the same metal, is passed 
through the cork of a small glass 
jar, or a large-sized vial, from which 
the bottom has been removed and 
its place supplied by a disc of wood ; 
and to the lower end of the wire, 
which may be slightly flattened, is 
attached, by means of any adher- 
ing substance, two narrow strips of 
gold leaf so as to bang freely, and 
when un-excited parallel to each 
other without touching. Two small pith balls suspended 
close together by threads a few inches in length may be em- 
ployed, in place of the gold-leaf strips. 

When we wish to ascertain if a body is electrified, 'or 
whether different parts of it are charged positively to the 




318 WRITINGS OP JOSEPH HENRY. [1855- 

same degree for example, we bring in contact with the part 
to be examined a small metallic ball suspended at the end 
of a very fine silk thread, (a fibre from a cocoon will serve 
for this purpose,) and afterwards bring the small ball, which 
may be called the carrier, in contact with the ball, or as it is 
called, the knob of the electroscope. The electricity of the 
carrier will distribute itself, on account of the repulsion of 
its atoms, throughout the knob, the stem, and the leaves of 
the electroscope. The leaves being the only movable part 
will diverge from each other, and will thus exhibit the elec- 
trical repulsion to the eye. We see from this experiment, 
as well as from that of the ball touched with the excited 
glass, that electricity may be transferred from one body to 
another, and that when it is applied to the end of an elon- 
gated metallic conductor it instantly diffuses itself over the 
whole mass. In the experiment we have just described, the 
body was supposed to have been positively electrified ; but a 
similar effect would have been produced had it been nega- 
tively charged. In that case, a portion of the natural elec- 
tricity of the carrying ball would have been drawn from it 
by the un-saturated matter of the electrified body, and the 
ball in turn, when brought in contact with the upper end of 
the electroscope, would draw from it a portion of its natural 
electricity — the deficiency extending to the leaves — which 
would therefore diverge, since according to the theory un- 
saturated matter repels un-saturated matter. 

If we wish to ascertain whether a body is electrified nega- 
tively or positively, we transfer a portion of its charge to the 
electroscope by means of the carrying ball, and then, hav- 
ing rubbed a rod of glass with a piece of woollen cloth, wo 
bring it near to the electroscope; if the leaves diverge farther 
when the rod of glass is brought near, the original charge is 
of positive or plus electricity ; if on the contrary the leaves con- 
verge, wo may consider the electricity as negative or minus; or 
the same conclusion may be arrived at by rubbing a stick 
of sealing-wax with the woollen cloth, which becoming nega- 
tively excited will cause the leaves in the case of a positive 
charge to converge, and in that of a negative charge to 
diverge. 



-1859] WRITINGS OP JOSEPH HENRY. 319 

Condvdicm and IrmdaJtion of Electricity, — ^By means of a 
simple electroscope of the kind we have just described wo 
may at once determine whether a body is a conductor or 
non-conductor of electricity. If a slight charge be given to 
the electroscope, (which may be eflfected by touching the 
knob with a rod which has been rubbed by woollen cloth,) 
the charge will remain with but little diminution for several 
hours, provided the air is perfectly dry; while if the air is 
moist, the charge is soon dissipated. These facts show that 
the former is a non-conductor, and the latter a partial con- 
ductor. Dry air would be a perfect insulator of electricity, 
provided it were motionless; the atoms which impinge 
against a charged body however become electrified with the 
same kind of excitement, and are consequently repelled, 
their place being supplied by others and so on until the 
charge is gradually diminished and finally dissipated. 

If, when the electrometer is charged in dry air, we touch 
the knob with a glass rod, the leaves will be but little affected; 
but if we breathe on the surface of the rod, the glass will be- 
come a partial conductor and the leaves will slowly converge. 
If the ball be touched with one end of a metallic wire, the 
electricity will instantly be conducted off. If we make a simi- 
lar experiment with a piece of dry wood, the charge will be 
gradually dissipated, a fact which indicates that wood is a 
partial conductor. By increasing the length of an imperfect 
conductor we shall find that the time of drawing off the 
charge is increased, and in this way it may be shown that 
there are very few bodies which are perfect conductors or 
non-conductors; that every body offers some resistance to 
the passage of an electrical current, provided wo increase 
the length suflBciently to make it perceptible. By experi- 
menting on various bodies in the way we have described, 
we may form an approximate table of the degrees in 
which different substances are conductors or non-conduc- 
tors of electricity. The human body is a very perfect 
conductor of ordinary electricity, since if we touch the knob 
of the electroscope with the finger, the leaves instantly col- 
lapse, provided we are standing on the ground at the time. If 



320 WRITINGS OF JOSEPH HENRY. [1855- 

however we place a non-conductor (for example a cake of bees- 
wax) under the feet, the whole of the charge will probably 
iiot be withdrawn but shared with the body, and the leaves 
will only partially converge. It may also be shown by the 
same instrument that in order to produce electrical excite- 
ment by friction, it is only necessary that two dissimilar sub- 
stances be rubbed together, one at least of which must be a 
partial conductor. For example, if while a person is stand- 
ing on a cake of bees-wax he place one finger on the knob of 
an electroscope and another person strike him on the back 
with a silk handkerchief, the leaves will instantly diverge 
showing that the whole body has received a charge of elec- 
tricity, which is prevented from escaping into the floor by 
the interposed non-conducting bees-wax. 

After the introduction of furnaces for heating rooms by 
warm air, the public was surprised at exhibitions of elec- 
trical excitement which previously had not been generally 
observed. If our shoes be very dry and we move over the 
surface of the carpet with a shuffling motion on a very cold 
day, (particularly in a room heated by a furnace,) the friction 
will charge the body to such a degree that a spark may be 
drawn from the finger, and under favorable circumstances 
a jet of gas from a burner may be thus ignited. There is 
nothing new or wonderful in this experiment; it is simply 
an exhibition of the production of electricity by friction, 
which only requires the carpet, the shoes, and the air to be 
dry, conditions most perfectly fulfilled on a day in which the 
moisture of the air has been precipitated by external cold and 
its dryness increased by its passage through the flues of the 
furnace. In the ordinary state of the atmosphere, the elec- 
tricity which is evolved by friction is dissipated as rapidly 
as it is developed, but in very cold weather the non-conduct- 
ing or insulating power of the air is so much increased that 
the electricity which is excited by the almost constant rub- 
bing of bodies on each other, is rendered perceptible. Every 
person is familiar with the fact that on removing clothes, or 
shaking garments in cold dry weather, the electricity evolved 
by the rubbing exhibits itself in sparks and flashes of light. 



-l8S9] WRITINGS OF JOSEPH HENRY. 321 

The popular idea in regard to this is that the atmosphere 
at such times contains more electricity than at others ; but 
these appearances are not due to the variation of the elec- 
tricity in the atmosphere, but simply to the less amount of 
vapor which is present. When the clothes are rubbed to- 
gether one part becomes positive and the other negative, and 
in dry air the excitement increases to such an intensity that 
the restoration of the equilibrium takes place by a visible 
spark; but when the air is moist, the equilibrium is silently 
restored as soon as it is disturbed, and no excitation is per- 
ceptible. 

Similar effects are observed on the dry plains of the western 
part of our continent : in rubbing the horses or mules, sparks 
of electricity may be drawn from every part of the body of 
the animal. Persons in delicate health, whose perspiration 
is feebly exhaled, sometimes exhibit electrical excitement in 
a degree sufficient to surprise those who are not familiar 
with the phenomena. But these exhibitions have no con- 
nection with animal electricity-, and are merely simple illus- 
trations of the electricity developed by friction in an atmos- 
phere too dry to permit the usual immediate and silent res- 
toration of the electrical equilibrium. 

Distribution of Electridtij. — ^The mutual repulsion of the 
atoms of electricity, varying inversely as the square of the 
distance, gives rise to the distribution of the fluid in regular 
geometrical arrangements, the form of which may bo calcu- 
lated with mathematical precision. As one of the simplest 
cases of distribution, suppose a conductor of the form of a 
cylinder, with hemispherical ends (for example, one of wood, 
covered with tin foil) to be suspended horizontally in dry air 
with s^k threads, and thus insulated to be slightly electri- 
fied by touching the middle of it with a charged body ; the 
atoms of the fluid, by their mutual repulsion, will separate 
as far as possible from each other, and be found at the two 
extremities. If the conductor were not surrounded with a 
non-oonducting fluid, like the air, they would be driven off 
by the same repulsion into space, and thus indefinitely 
separated. 

21-2 



322 



WRITINGS OF JOSEPH HENRY. 



[1855- 



This inference from the theory can readily be proved to 
be in accordance with the actual condition of the excite- 
ment, by bringing into contact with the middle of the length 
of the conductor a small carrier ball, and afterwards apply- 
ing it to the knob of the electroscope. If the charge given to 
the conductor be small, scarcely any electricity will be found 
at the middle ; if however the carrier be brought into con- 
tact with either end of the conductor, it will receive a charge 
of such intensity as to cause the leaves to diverge widely 
from each other. If a charge of electricity be imparted to 
the centre of a conductor in the form of a thin circular disc 
the fluid will bo found, by a similar examination, in the 
greatest intensity, at the outer rim. 

If we electrify a solid globe of metal, the excitement will 
be confined to an indefinitely thin stratum just at the surface 
of the conductor; for if the electricity be imparted to tho 

centre of tho globe along a wire 
through a glass tube, the electri- 
cal atoms will evidently separate 
from each other as far as possible, 
on account of their mutual repul- 
sion, and would continue to di- 
verge even beyond the surface, 
were it not that they were stopped 
by the non-conducting air which 
surrounds and insulates the globe. 
That this inference is true may be 
shown by an arrangement which 
is exhibited in Fig. 3, in which A 
represents a hollow metallic globe 
insulated on a glass pillar and 
charged with electricity. If the 
carrier ball B be let down into 
the interior of the globe, so as to 
touch the inner surface and then 
withdrawn without touching the 
side of the hole it will be found 
entirely free from electricity. If however it be made to 




-1859] 



WRITINGS OF JOSEPH HENRY. 



823 




toucl} the outside of tbe globe, it 
will carry off with it a charge 
which will cause the leaves of the 
electroscope C to diverge in pro- 
portion to the original quantity 
imparted to the sphere. A simi- 
lar effect will be exhibited if the 
ball B be lowered into an insulated 
cylinder of wire gauze A, Fig. 4, 
which has been charged with elec- 
tricity. Not the least sign of ex- 
citement will be found on the in- 
side, while a spark may perhaps 
be drawn from the exterior. The 
same result is produced, (as will 
be seen,) whether the 'globe be 
charged negatively or positively. 
On thje hypothesis that the attrac- 
tion and repulsion both observe 
the law of diminution with the 
square of the distance, this curious j,^^ ^ 

phenomenon is readily explained. 

Newton has demonstrated the following propositions 
relative to the action of gravitation; and these principles 
are equally applicable to electrical attraction and repulsion, 
or to any other action which varies inversely as the square 
of the distance: 

1. A particle of matter placed outside of a hollow sphere 
of attracting or repelling matter of uniform thickness, is 
acted upon as if all the matter were concentrated at the 
centre of the sphere. 

2. A particle of matter (or of free electricity) placed at any 
point within a hollow sphere of uniform attracting or repel- 
ling matter, will be acted upon in every direction by an 
equal force, and will consequently be in equilibrium. 

The form of the demonstration of the first of these propo- 
sitions may be easily understood by a reference to Fig- 
ure 5, and thfs accompanying considerations: 




324 



WBITINOS OF JOSEPH HEMRT. 



[1BS5- 




In this figure, a represents a par- 
ticle of matter or of electricity at- 
tracted or repelled by the hollow 
sphereofwhichthecentreisC Let 
the two liues a d and a e represent 
the projection of a pyramid hav- 
ing its apex iu o, and its haae in 
d e, then it will bo evident that 
the attraction of the three sections 
of the cone, one through the cen- 
tre, another coinciding witli the 
upper part of the spherical shell, 
and the third with the lower part 
included within d e, will he equal. 
For although the lower section is 
at a greater distance from o than F". 5. 

the upper, yet its greater size just compensates for the greater 
distance, the surface increasing, as in the case of light, as the - 
square of the distance, while the attraction and repulsion 
diminish in the same ratio. For the same reason, each of the 
two portions of the spherical shell are equal iu action to a plate 
of equal thickness through the centre, included within the 
cone; and hence, the two together will be equal to a plate 
of double thickness at the centre. 

If in the same way we suppose the whole spherical shell 
included in a scries of pyramids or cones, having as a common 
apex the point a, and consider this series of cones made up 
of equi-angular pairs, the two members of which are oo each 
side of the line through the centre ash ai, and fag, then it 
will be clear that the resultant action of each of these pairs of 
cones will be in a line through the centre, and all the action 
of the sphere made up of such coues the same as if it were 
at this point. 

That a point at the centre of a hollow sphere would be 
equally acted upon in all directions is evident; hut that the 
same should be the case when the point is at a, Fig. 6, for 
example, is not quite so clear. It may however he rendered 
evident by considering the actions of the opposite bases of 



326 WRITINGS OF JOSEPH HENRY. [1855- 

chargcKl surface; and for. a similar reason, when the globe is 
charged negatively, to draw in electricity from surrounding 
bodies. 

From the second proposition, we can readily deduce the 
fact of the distribution of the electricity at the surface ; for 
if we communicate to the interior of a globe a quantity of 
electricity just sufficient to arrange itself in a stratum of the 
thickness of a single, particle, it will so arrange itself on 
account of the mutual repulsion of the atoms, but if an 
additional quantity is thrown into the interior, it might not 
appear evident that this would also come to the surface, since 
the repulsion of the atoms already' at the surface, (as it would 
seem at first sight,) would drive the additional atoms back 
towards the centre; but from the second proposition, the 
inner atoms are notaflfected by the outer, and consequently 
they would separate from each other by their mutual re- 
plusion, as if the latter did not exist, and arrange themselves 
at the surface. 

That this should take place when the sphere is charged 
with redundant electricity is not difficult to understand; 
but when a deficiency exists, the explanation has not 
been thought as easy. If however we suppose a quan- 
tity of the natural electricity drawn from the interior of 
a solid globe, then the un-saturated matter in the centre of 
the globe will act as a sphere, and draw into itself the elec- 
tricity from around, and thus produce a hollow sphere of 
attracting matter, which will again draw into itself the 
natural electricity from around, and in this way, it must be 
evident, the deficiency will finally come to exist at the sur- 
face. 

These propositions, which as we shall see are of great im- 
portance in the study of the theory of atmospheric electricity, 
can be readily demonstrated experimentally. If we coat a 
large hollow glass globe with tin foil, and insert through an 
opening into it a delicate electroscope, consisting of two slips 
of gold leaf suspended parallel to each other, (a small piece 
of the covering of tin foil being removed at two points on 
opposite sides to observe any effects produced within,) not 



-1859] WRITINGS OP JOSEPH HENRY. 327 

the slightest divergence will be seen in the gold leaves, when 
the globe outside is intensely charged with electricity. The 
same result will be obtained when a slip of gold leaf is sus- 
pended in the interior and electrified, either positively or 
negatively. It does not follow from these experiments that 
the electricity on the outside does not act on that of the in- 
side. On the contrary, we must infer.from the theory that 
every atom of electricity at the surface acts repulsively on 
every atom of electricity in the gold leaf; but these actions 
are equal in all directions, and therefore neutralize each 
other. 

The second proposition may be demonstrated by means 
of a charged ball and the hollow globe. Fig. 3. If the 
charged ball, suspended by a silk thread, be placed at about 
eighteen inches above a gold leaf electroscope, and the diverg- 
ence noted, and if then the ball be removed and its place 
occupied by the centre of the globe to which the electricity of 
the ball has been imparted, the divergence will be the same 
as before ; or in other words, the action on the electroscope 
will be the same when a given quantity of electricity is con- 
centrated on a ball at the centre of a sphere, or diffused 
throughout the surface of the same body. This experiment 
may be varied, with more striking results, by placing the 
hollow globe at a given distance from the electroscope, and 
then letting down a charged ball into its interior until it 
reaches the centre: the leaves will be seen to diverge to a defi- 
nite degree; if the ball be now made to strike the interior sur- 
face of the globe, by moving the suspending thread of silkt 
the whole of the charge will pass to the surface of the latter, 
but the leaves will exhibit the same amount of divergence as 
before the transfer. The electricity which is distributed 
throughout the surface of the globe .produces precisely the 
same effect as it did when confined to the ball at the centre. 

The mathematical problem to be solved, for the purpose 
of calculating the distribution of a given charge of elec- 
tricity in a body of any form, is to proportion the amount of 
the fluid in each part of the surface, so that the resultant 
action on the interior of a body will be completely neutra- 
lized. This problem, which is sinxple for the sphere, becomes 



828 



WRITINGS OP JOSEPH HENRY. 



11355- 



too complex, even for the highest powers of mathematics, 
for bodies of less regular forms than those generated by the 
revolution of simple curves. 

Electrical Induction. — The attraction and repulsion of elec- 
tricity, like those of magnetism, act at great distances, and 
produce phenomena which it is necessary clearly to under- 
stand in order properly to comprehend the explanation of 
many of the facts connected with atmospheric electricity. 

For the exhibition of these phenomena, which are classi- 
fied under the name of inductive eflTects, we may make use 




^ 




FiQ. 8. 



of the arrangement represented in Fig. 8, in which -4 is a 
metallic globe suspended in free air by a fine silk thread, and 



-1859] WRITINGS OP JOSEPH HENRY. 329 

thus insulated. is a long cylindrical metallic conduc- 
tor, supported by a rod of shellac or sealing-wax d, on stand 
e, having a glass stem. 

Now each of these metallic bodies contains its natural 
share of electricity, and as long as this continues to be the 
same no electrical effects are exhibited; for although the 
natural electricity of A will repel the electricity of 0, yet .the 
matter of A will attract it with an equal force, and hence 
there will be no perceptible effect. Let us however suppose 
that there be imparted to the globe A a redundant quantity 
of electricity, then the equilibrium in the conductor will 
be disturbed; the repulsion of the redundant fluid will be 
greater than the attraction of the un-saturated matter, and 
hence a portion of the natural electricity of will be driven 
down to its lower end, and consequently the upper end will 
become negatively, while the lower is positively electrified. 
It must be evident therefore that between the two extremes 
there will be a point near the middle which will be in its 
ordinary condition. 

These inferences may readily be shown to be true by 
observing three movable pith balls suspended 'by linen 
threads, one near the top, another at the middle, and the 
third at the lower end. Those at the extremities will 
diverge, exhibiting excitement, while the one at the mid- 
dle will remain unmoved, indicating that this point is 
in a natural condition. To be assured that the upper end 
is negatively electrified, and the lower positively, it is only 
necessary to rub a stick of sealing-wax with woollen cloth, 
and bring it in succession near the two balls ; the upper 
one will be repelled and the lower one attracted ; or we may 
arrive at the same results by touching in succession the two 
extremities and the middle of the conductor with the small 
carrier ball a, and applying it to the knob of the electro- 
scope B, 

If the conductor be removed laterally to a distance from 
under the charged globe, the excitement will disappear, the 
atoms of natural electricity, by their mutual repulsion at 
the lower end, and attraction for un-saturated matter at 



330 WRITINGS OF JOSEPH HENRY. [1855- 

the upper end of the conductor, will distribute them- 
selves uniformlv, and assume their natural condition. In 
this experiment -the fact is illustrated that all bodies are 
naturally charged with electricity, which exhibits itself 
when the equilibrium is disturbed by the action of some ex- 
traneous force. If the conductor be restored to its former 
position the excitement will be renewed, provided the globe 
A has lost none of its charge, and the two pith balls will di- 
verge as before. If the charge of electricity in the insulated 
globe be increased, the repulsive action or induction, as it 
is called, will also be increased ; another portion of electri- 
city will be impelled down into the lower end, increasing the 
repulsive action at that point, and also the amount of attrac- 
tion at the upper end. The middle of the conductor however 
will still remain in a condition of neutrality. Again, if while 
the charge in the globe A remains the same, the space be- 
tween it and the upper end of the conductor is diminished, a 
greater excitement will be exhibited by the increased diver- 
gence ot tlie balls at the two extremities ; for since the force 
increases with a diminution of distance, an additional quan- 
tity of the natural electricity of the upper end will be driven 
down into the lower end, and an equal amount of un-satu- 
rated matter will be left at the upper end. 

We may still further vary the experiment by lengthening 
the conductor 0, the charge of Uie globe and its distance 
from the upper end remaining the same, and for this pur- 
Ix)so the conductor may be made to draw out like the tube 
of a telescope. We shall find that the greater the length, 
the greater will be the intensity of the eflect at each end. 
To understand this we have only to recollect that the atoms 
of electricity constantly repel each other, and that in the 
case of a short conductor, but little comparatively can ^e 
driven from the upper end, because the self-repulsion of 
the electricity of the lower end and the attraction of the 
un-saturated matter of the upper end both conspire to restore 
the distribution, but when we give a greater length to the 
conductor for the free electricity of the lower part to expand 
into, and thereby lessen the intensity of the repulsion and 



-1859] WRITINGS OP JOSEPH HENRY. 331 

also remove the free electricity farther from the centre of 
attraction of the redundant matter, the tendency to restore 
the normal condition is much lessened, and a new quantity 
will be repelled into the lower end from the upper, and thus 
produce at that end a greater intensity of excitement. If 
we increase indefinitely the length of the conductor, (or what 
amounts to the same thing) if we connect the lower end of 
it by means of a metallic wire or other conductor with tlie 
earth or elongate it till it touches the earth, then we shall 
have the maximum of effect. The neutral point will descend 
to the earth, while the conductor, thoughout its entire length, 
will be charged negatively. 

The efiects which we have described are those which would 
take place if we supposed the electricity in the globe suffered 
no change in its distribution on account of the induction ; 
but this cannot be the case, since in the action of one body 
on another — an equal re-action must be produced, hence the 
un-saturated matter in will re-act on the free electricity in 
the globe, and draw down into its lower side a portion of 
that which before existed in the upper side, and thus render 
the lower side more intensely redundant than before. This 
additional quantity of free electricity in the lower side will 
tend to increase the amount of un-saturated matter in the 
upper part of the conductor. The maximum effect will be 
produced, as we have before stated, when tlie lower end of 
the conductor is brought in contact with the earth, which 
may be considered as a conductor of infinite capacity. In* 
this condition the self-repulsion of the atoms of the fluid in 
the lower part of the globe, and the attraction of the un- 
saturated matter in the upper end of the conductor, may 
become so great as to cause a rupture of the intervening air 
and a transfer of the redundant electricity in the form of 
a spark from the upper to the lower body. 

If instead of the metallic conductor we substitute a rod 
of shellac or glass of the same length and diameter under 
the same conditions, no spark (or but a voi-y feeble one) will 
be produced. Tlie natural electricity cannot be driven 
down on account of the non-conduc-ting character of the 



332 



WniTINOS OF JOSEPH HSNBT. [1855- 



material, and while it remains at the top it repels the free 
electricity of the globe as much as the matter of the globe 
attracts it. For a similar reason, if a small brass ball be 
placed on the top of a rod of glass and presented to the 
globe, but a feeble spark will be elicited ; the inductive in- 
fluence will act in this case under unfavorable conditions, a 
portion of the natural electricity, it is true, will be driven 
down into the lower surface of the ball, and an equal amount 
of un-saturated matter will exist at the upper surface ; but 
the attractions and repulsions will be so nearly at the same 
distance that but a comparatively feeble eflect will be pro- 
duced. An attentive consideration of these facts is essential 
to a knowledge of atmospheric electricity, and necessary to 
understand and guard against the efiects of the destructive 
discharges from the thunder-cloud. 

The inductive action we have described takes place at a 
distance through an intervening stratum of air, but the same 
effect is produced, and with nearly the same intensity, when 
the intervening space is occupied with glass or any other 
non-conducting substance. If a disk of wood, which is a 
partial conductor, is interposed, the effect will be slightly 
modified, because an inductive action will take place in the 
substance of this which will tend to increase the effect in the 
conductor 0, below. 

As an illustration of the inductive influence of free elec- 
tricity at a distance on the natural electricity of a conduc- 
tor, we shall direct the attention of the reader to an arrange- 
ment exhibited in Figure 9, which is that of an experiment 
made by the author in Princeton, in 1842*. Two circular 
disks of wood, a and 6, each about 4 feet in diameter, 
were entirely covered with tin foil; one was in connec- 
tion with a large insulated conductor of an electrical ma- 
chine in the upper story of a building, the other was sup- 
ported on a glass foot in the lowest story, at the distance 
of about 25 feet below, with two floors and ceilings interven- 
ing. The upper disk being charged by the machine, the 
lower one was touched with the finger, so as to suffer -the in- 

* [Proceedings Am. Phil. Society, June 17, 1842. See anUf vol. i, p. 208.] 



-1859] 



WRITINGS OF JOSEPH HENRY. 



333 



duced electricity to escape into the ground. If when in this 

condition the knuckle was 
held near the lower disc 
and the upper one suddenly 
discharged by a spark re- 
ceived on a ball attached to 
the end of a wire connected 
with the earth, a spark was 
seen to pass between the 
knuckle and the lower disk. 
A similar eflfect was pro- 
duced when the upper plate 
was suddenly charged by 
powerful sparks from the 
machine, though the inten- 
sity in this case was some- 
what less. 

In this experiment, the 
upper disk may represent a 
charged thunder-cloud, and 
the lower one the ground, or 
any conducting body with- 
in a house. While the 
charged cloud is passing over the building, all conducting 
bodies in it,^by this inductive action at a distance, have 
their natural electrical equilibrium disturbed; the upper 
part of each body becoming negatively electrified, and the 
lower part positively ; and if the cloud continue in this 
position for a few minutes, the free electricity of the lower 
part of the conductor will be gradually driven into the 
earth, through the imperfect insulation of the floor. If in 
this case the lower part of the cloud is suddenly discharged, 
sparks of electricity may be perceived, and perhaps shocks 
experienced, by the inmates of the dwelling, produced by 
the sudden restoration of the equilibrium, due to the removal 
of the repulsive force of the cloud on the natural electricity 
of the bodies b^ow. 
The inductive action of the electrical discharge at a dis- 




Fio. 9. 



834 



WRITINGS OF J08BPH nENRT. 



[1S95- 



tauce is still more surprisingly exhibited, by an armngemcnt 
shown in Figure 10, which the writer adopted about the 
same time during his electrical investigations at Princeton. 

The roof of the house 
which he occupied in the 
college campus was cov- 
ered with tinned iron, and 
this covering was there- 
fore in the condition of 
an insulated plate, on ac- 
count of the imperfect 
conduction of the wood 
and brick- work which in- 
tervened between it and 
the ground. To one of 
tlie lower edges of this 
covering was soldered a 
copper wire, which was 
continued downward to 
the first story, passed ^ 
through a gimlet-hole in 
the window-frame into 
the interior of the author's study, and then passed out of 
the lower side of the same window, and thence into a well, 
in which it terminated in a metallic plate below the surface 
of the water. Within the study, the wire was cut and 
the two ends tlius formed were joined by a spiral of finer 
wire a covered with silk thread. Into the axis of this spiral 
a large sized sewing-needle d was inserted, the point having 
been previously attached to a cork, which served as a handle 
for removing it. With this arrangement, the needle was 
found to become magnetic whenever a flash of lightning 
was perceived, though it might be at the distance of several 
miles. The intensity of magnetism and the direction of the 
current were ascertained by presenting the end of the needle 
to a small compass represented by c. In several instances 
the inductive action took place at such a distance, that after 
seeing the flash the needle was removed its magnetic con- 




Fio. 10. 



-1859] WRITINGS OF JOSEPH HENRY. 335 

dition observed and another needle put in its place, before 
the noise of the thunder reached the ear. In this experi- 
ment the inductive action of the electrical discharge in the 
heavens was exerted on the natural electricity of the tinned 
roof, (a surface of 1,600 square feet,) and a considerable portion 
of this passed down through the wire into the well. The 
arrangement served to indicate an action which would 
otherwise have been too feeble to produce a sensible impres- 
sion. 

It must be observed that the effect here described was not 
produced by the actual transfer of any electricity from the 
cloud, but was simply the result of induction at a distance 
and would probably have been nearly the same had the in- 
tervening space been filled with glass or any other solid 
non-conducting substance. We say probably very nearly the 
same, because Professor Faraday has shown that the induc- 
tive effect at a distance is modified by a change in the in- 
tervening medium. 

It is also proper to mention here, (although we cannot 
stop to give the full explanation of the means by which 
the result was obtained,) that the electricity passing along the 
wire was not that due to a single discharge into the well, 
but to a series of oscillations up and down in alternate direc- 
tions until the equilibrium was restored. 

* 

EledricUy in Motion. — The phenomena we have thus far 
described relate principally to electricity at rest. Those 
which relate to ordinary or frictional electricity in motion 
liave not been so minutely investigated as the other class, 
and present much more difficulty in ascertaining the laws 
to which they are subjected. The discharge of electricity 
from the clouds or from an ordinary electrical machine is 
80 instantaneous that we are principally confined in our in- 
vestigations to the effects which remain along its path after 
its transfer. 

The electricity however which is developed by chemical 
action in a galvanic battery is of sufficient quantity to pro- 
duce a continuous stream, or at least a series of impulses in 
such rapid succession that they may be considered continuous. 
By employing electricity of this kind, it has been supposed 



G5 OF JOSEPH HENRY. [1855- 

-VI- V-: c;kn r: - !y the fluid while it is actually iu motion, and 
i-:n ii-: rs^-^I*^ deJuee inferences as to the mode in which 
f^.c:- . : :iv vffeots are pro«Juced in the discharge of frictional 
^l>::-...:7 The two classes of phenomena however, though 
r::Tri:'.v :o :he same cause, are in many respects so diflfer- 
tz.: :- .lirjcier that considerable caution is required in 
Lri'T.^ inrVrtncx-s from analogy. The phenomena of ordi- 
zjsj c'.-vtricity are characterized by an intensity of action 
t1::1 izlicait-s a repulsive force between the atoms of the 
Ijrt: :h: :;oal iluid, which is in some way — ^at least partially 
z.^c:r-I::eJ. in the case of galvanism. 

Oriinary electricity in a state of equilibrium appears 
V rr^i-oe but a very feeble effect upon bodies in which 
:: :< i-.vumulated. However great may be the quantity 
rrs^n:. no effect is perceived by a person when insulated 
*c i glass stool, and charged either positively or nega- 
TiTt'y. so long as the electricity remains at rest If how- 
t-r^r i: is drawn from him in the form of a spark, then a 
Jisi^x'able pricking sensation is experienced at the point 
cc r-pvjre. Dr. Faraday constructed a small metallic house 
or rvs?!i3. which he suspended by silk ropes in mid air, 
«ni chanrod it so strongly that long sparks could be 
craw:: fn.»m the outside, yet not the least effect was perceived 
; V ;he jvrst^ns within: even when the air of the interior of 
•.ho hoUM? was strongly electrified, the excitement was only 
'x^x'P'iblo on the outside. 

Ii is fully established by the most satisfactory experiments 
:ha: in all cases in which a discharge of electricity takes 
ridce bv breaking through a stratum of non-conducting sub- 
unce like air, there is an actual transfer of matter each way 
Mweon the two ends or sides of the opening in the conduc- 
lor alon*'' the path which the spark traverses. If two con- 
Juoung rods be employed having the end of each termi- 
iMted bv a brass ball, one of which is covered with gold leaf, 
*nJ the" other with silver, a transfer in opposite directions 
if these two metals will be observed. A similar effect is pro- 
daced in the discharge of lightning from the clouds, and 
theTO aw several well authenticated cases on record, in 



-1859] WRITINGS OF JOSEPH HENEY. 337 

which a picture as it were of one body has been impressed on 
another between which the electrical discharge took place. 

Another effect produced by the discharge, and having an 
important bearing upon the . explanation of some of the 
mechanical results of electricity, is a sudden and violent 
repulsive energy given to the atoms of air and other sub- 
stances through which it passes, and which causes them to 
separate with an explosive violence. 

This may be shown by transmitting a discharge from an 
electrical battery between two brass balls projecting into the 
inside of a glass bulb, to the lower side of which is joined 
an air-tight tube containing a small quantity of water, and 
opening at the end into a cup of water, the arrangement 
with the exception of the balls being similar to that of an 
air thermometer. The moment the discharge takes place, 
the water will be driven down the tube, exhibiting a great 
enlargement of the volume of air in the bulb. This experi- 
ment was communicated by Mr. Kinnersloy, of Philadelphia, 
to Dr. Franklin. The effect at first was attributed to heat 
produced by the discharge of electricity through the air ia 
the bulb, but although there wheat evolved in this case, (as 
is proved by the fact that if a number of sparks be passed in 
succession the water does not return to its first altitude, and 
thus indicates an increase of temperature,) yet the princi- 
pal cause is evidently the sudden repulsive energy given 
to the air at the moment of the passage of the discharge, 
as may readily be shown by inclosing a thermometer 
within the bulb. The increase of temperature which this 
indicates will be far too small to account for the great 
and sudden expansion produced. A similar exhibition of 
force is exhibited when a strong discharge of electricity 
is passed through a vessel (like the one we have described) 
filled with water. In this arrangement a thick glass bulb 
may be broken into pieces. 

The mechanical effects produced by lightning must be 
attributed principally to this cause. When a powerful dis- 
charge from a cloud passes through a confined space filled 
with air, and surrounded by partial non-conductors, a trc; 

22-2 



338 WKITINQS OF JOSEPH HENRY. [1855- 

mendous energy is exerted. In the case of a house examined 
by the writer, the discharge fell upon the top of a chimney 
at the west end of the building and passing through a stove- 
pipe hole traversed the space under the rafters, (called the 
cock-loft), to the chimney at the east end and thenoe down 
to the ground ; the force exerted was suflBciently great to 
lift up the whole roof from the top of the walls on which it 
rested. In like manner, when the discharge takes place 
along the upright timbers of a house, the clap-boards are 
frequently blown off outward and the plaster inward as if 
by the explosion of gunpowder. 

To a similar action we must ascribe the splintering of trees 
•by lightning. At the moment of the passage of the dis- 
charge the sap or moisture is suddenly endowed with a re- 
pulsive energy which resembles in its effects the action of 
an explosive compound, separating the fibres longitudinally 
and projecting parts of the body of the tree to a distance. 
When a tree is struck by lightning the greatest effect is 
usually produced on the main stem just below the branches. 
A portion of the discharge appears to be received on each 
twig, leaf, and branch, and the whole concentrated by con- 
verging towards the trunk. The repulsion imparted to the 
atoms of a conductor is in some cases sufficiently great to 
at once dissipate in vapor fine metallic wires, and this so 
instantaneously that thd silk covering by which they are 
surrounded for telegraphic purposes is not burned. 

The repulsive energy is exerted not alone laterally, but 
perhaps in a greater degree in the line of direction of the con- 
ductor, tending to separate it as it were by transverse sec- 
tions. Hence when electricity passes through a wall into 
the interior of a house, a pyramidal mass of plaster is thrown 
out. A similar effect is frequently produced when the dis- 
charge takes place between the cloud and the level earth : a 
large conical or pyramidal hole is formedj from which the 
earth is thrown out as if by the explosion of a quantity of 
powder beneath the surface. Such excavations are sup- 
posed by some to indicate a discharge of electricity from the 
earth to the cloud, but no conclusion of this kind can, with 



-18591 WRITINGS OF JOSEPH HENRY. 339 

certainty, be drawn from the phenomena. It simply indi- 
cates an intense repulsive energy exerted between the atoms 
of matter in the linQ of discharge. It sometimes happens 
when an old tree which has perhaps been moistened by the 
rain — is struck by lightning, instead of being rent laterally 
it is broken off transversely, the upper part being projected 
vertically upward. This effect however is not usually pro- 
duced, since the force exerted by the tree to resist trans- 
verse' breaking is much greater than that to prevent lateral 
tearing apart 

In the passage of electricity from a charged conductor, or 
from a cloud to the earth, it always follows the line of least 
resistance and bv an antecedent induction determines the 
course it is to pursue. This is strikingly exhibited by an 
experiment devised by Sir W. S. Harris. A number of sepa- 
rate pieces of gold leaf are attached to a sheet of paper. If 
a discharge sufficiently strong to dissipate the gold and 
blacken the paper be passed through them, its course will 
be shown by the blackened parts ; and it is especially worthy 
of remark, that not only are the pieces out of the line of 
least resistance untouched, but even portions of other pieces 
are left unchanged from the same cause. Now these sepa- 
rate pieces of gold leaf may be taken to represent detached 
conductors fortuitously placed in the construction of a 
building. 

The apparently fitful course of a discharge in its passage 
through a building frequently excites surprise, leaping (as 
the electricity does) from one conductor to another, and 
sometimes descending to the earth in several streams ; but 
that the discharge should leap from one conductor to another 
through a considerable intervening space of air is not sur- 
prising, since its original intensity was sufficient to enable 
it to break through a stratum of the atmosphere of perhaps 
a mile in thickness before it reached the house. 

Whenever electricity passes through an interrupted con- 
ductor so as to exhibit the appearance of light, a great in- 
crease of intensity is always manifested at the point of dis- 
ruption, as if the charge halted here for a moment until a 



340 WRITINGS OF JOSEPH HENBT [1855- 

sufficient quantity of the fluid could accumulate to force its 
passage through the obstacle. An illustration of this action 
is presented in the fact, that at the point where the lightning 
leaves a conductor, and also where it is received by another 
conductor, signs of fusion or of more intense action are al- 
ways exhibited. An effect of lightning described by Pro- 
fessor Olmsted, at a meeting of the American Association, 
in New Haven, may be explained on this principle. A row 
of five or six milk-pans, placed in the open air on a bench, 
was struck by a discharge from a cloud. The electricity 
passed through the whole series, making two holes in 
each pan, at opposite extremities of the diameter, or at the 
places where the electricity may be supposed to have en- 
tered and gone but. 

There is another circumstance connected with the dis- 
charge of electricity — having an important bearing on the 
construction of lightning-rods, which may be mentioned in 
this place. When the repulsion of the atoms of electricity 
in a conductor or in a cloud and the attraction of the un- 
saturated matter below become so intense as to cause a rup- 
ture in the air, the electricity of the cloud is precipitated 
upon the conductor, and not only restores the natural quan- 
tity, but also gives it for a moment a redundancy of elec- 
tricity, a fact which must be evident from the theory, when 
we consider the distance at which the induction is com- 
municated. As this charge of free electricity passes down 
the rod to the earth, for example, it assumes the charac- 
ter of a wave, rendering the metal negative in advance ; 
and thus in the transmission of free electricity through a 
rod of metal, the action consists of two waves, one of re- 
dundancy, immediately preceded by one of deficiency. 
Hence if a small ball connected with the earth by a wire be 
brought near a conductor (for example a lightning-rod) on 
the upper end of which, discharges of electricity are thrown 
from an electrical machine, sparks may be drawn from the 
rod, however intimately it may be connected with the earth 
below\ 

This efifect was strikingly exhibited by an experiment 



-1859] WRITINGS OP JOSEPH HENRy. 341 

made by the author, which consisted in placing one end 
of a copper wire (a tenth of an inch in diameter) beneath 
the water of a well, its upper end being terminated by a 
small ball, and throwing on it sparks of electricity from a 
globe of a foot in diameter. Although in this case the con- 
ductor was as perfect as possible, yet sparks suflBciently in- 
tense to explode the oxy-hydrogen pistol were obtained from 
the wire throughout its whole length. 

This eflFect was not due, as some have supposed, to the 
tendency of the electricity to seek another passage to the 
earth, as may be sho^i^n by catching the spark in a Leydcn 
jar ; but it was solely the effect of a transient charge of elec- 
tricity passing along the surface of a conductor from one 
extremity to the other. 

The phenomena may be expressed generally by the state- 
ment that when electricity is thrown explosively as it were, 
on the end of an insulated conductor, by a disruptive dis- 
charge through the arr, it does not pass silently to the 
earth, but tends in part to be given off in sparks to all 
surrounding bodies. It is on this account that we object to 
the otherwise admirable arrangement of Sir W. Snow Harris 
for the protection of ships from lightning. Though the 
main portion of the discharge of electricity is transmitted 
innoxiously to the ocean by means of the slips of copper 
which are carried down along the mast and through the 
bottom of the vessel to the sheathing beneath, as proposed 
by him, yet we consider it safer to conduct it across the deck 
and over the sides of the vessel to the copper sheathing. It 
is true, the quantity which tends to fly off laterally from 
the rod is small, yet we have shown by direct experi- 
ment that it is sufficient even when produced by the elec- 
tricity of a small machine, to set fire to combustible materi- 
als; and therefore it cannot be entirely free from danger in 
a ship, loaded for example with cotton. 

Tlie atoms of electricity, in their transfer from one body 
to another, still retain their repulsive energy ; and if the 
discharge be not very large in proportion to the size of the 
conductor, it will be principally transmitted at the surface. 



342 WRITINGS OF JOSEPH HENRT. [185S- 

If tho charge be very large, and the conductor small, it 
will probably pervade the whole capacity, and as we have 
seen, in some cases, will convert into an impalpable powder or 
vapor the solid particles. Because electricity in a state of 
rest is found distributed at the surface of a body, it was im- 
mediately assumed without examination, that electricity in 
motion passes along the surface ; but this conclusion was 
supposed to be dis-proved by the fact that the conducting 
power of a wire for galvanic electricity is in proportion to 
the area of the cross-section, from which it follows that this 
kind of electricity pervades the whole mass of the conduc- 
tor. But galvanic electricity differs from common electric- 
ity, apparently in the exertion of a much less energetic re- 
pulsion, and in a greater quantity developed in a given time. 
The deduction therefore from the experiments with galvan- 
ism can scarcely be considered as conclusive in regard to 
frictional electricity. 

To settle this point, the writer devised a series of experi- 
ments which fully proved the tendency of electricity of high 
tension, (that is of great repulsive energy,) to pass along the 
surface. It will be sufficient to give as an illustration of 
tliis fact, the result obtained by the arrangement represented 
in Fig. 11, in which (7 Z> is a copper wire, (one of the best 







Fig. 11. 



^ 



conductors of electricity,) of the size usually employed for 
ringing door-bells, passing through the axis of an iron 
tube, or a piece of gas-pipe, A By about three feet long. 
The middle of this wire was surrounded with silk, and 
coiled into a magnetizing spiral, into which a large sew- 
ing-needle was inserted. The wire was supported in the 
middle of the tube by passing it through a cork (covered 
with tin-foil), at each end, h i, so as to form a good me- 
tallic connection between the copper and the iron. Two 



-1359] WRITINGS OP JOSEPH HENRY. 343 

other magnetizing spirals of iron wire, / and t/, were ar- 
ranged on opposite sides of the tube, the ends soldered to 
the iron. When these two spirals were also furnished with 
needles, and a discharge from a Leyden jar sent through the 
apparatus, as if to pass along the wire, the needle inside of 
the iron tube was found to exhibit no signs of magnetism, 
while those on the outside presented strong polarity. This 
result conclusively shows that notwithstanding the interior 
copper wire of this compound conductor was composed of a 
material which offered less resistance to the passage of the 
charge than the iron of which the outer portion was formed, 
yet when it arrived at the tin-foil covering of the cork, it 
diverged to the surface of the tube, and still further diverged 
into the iron wire forming the outer spirals. We must not 
however conclude from this experiment that the electricity 
actually passed on the outside of the tube. On the contrary, 
we must infer from the following fact that it passes just 
within the surface. If the iron be coated with a thin cover- 
ing of sealing-wax, the latter will not be disturbed when 
a moderate discharge is passed through it, though with 
a large discharge in proportion to the conducting power of 
the rod, the outward pressure may become so great as to 
throw off the stratum of sealing-wax. This point is of some 
importance in regard to the question of painting lightning- 
rods. If the metal is of sufficient size to freely transmit an 
ordinary discharge from the clouds, the condition of the ex- 
terior surface can have but little effect, and we see no objec- 
tion to coating it with black paint, the basis of which is car- 
bon, a good conducting material. 

It is also to the same repulsive energy that we may at- 
tribute the spreading of a discharge wh^n it passes through 
partial conductors, as in the case in which a spark from an 
electrical machine is transmitted over a pane of glass on 
which particles of iron filings are sparsely scattered. It is 
probable that drops of rain and partiall)^ condensed vapor 
in the atmosphere are in some cases connected with a simi- 
lar appearance of discharge of electricity in the heavens. 
' A much longer spark of electricity can be drawn through 



344 WRITINGS OP JOSEPH HENRT. [185S- 

rarified air than through that of ordinary density. The 
light which accompanies a discharge in this case assumes 
diflFerent colors, the violet predominating. This is a fact of 
interest in connection with the color exhibited by lightning, 
and we may infer that the discharges of a violet hue take 
place between clouds at a great elevation in the atmosphere. 

The electric spark, when passed through a confined por- 
tion of atmospheric air, is found to produce a chemical com- 
bination of its component parts, namely nitrogen and 
oxygen, and to form nitric acid. The same result is pro- 
duced on a grand scale in the heavens during thunder- 
storms; hence the rain water that falls, (in the summer 
season especially,) always contains a considerable quantity of 
nitric acid, which is considei^ed by the chemist as furnishing 
a portion of the nitrogen essential to the growth and devel- 
opment of the plant : and to the same source is referred the 
nitric acid in the nitrate of lime and potash found in the 
form of efflorescence on damp ground and the walls of old 
buildings. Indeed, all the nitrate of potash from which 
gunpowder is manufactured is supposed to have its origin 
in this way, and the explosion from the thunder-cloud 
and that from the cannon, may be looked on as in one 
sense — the counterparts of each other. 

Again, during the transmission of electricity from an or- 
dinary electrical machine a pungent odor is perceived, some- 
thing analogous to that produced by the slow combustion 
of phosphorous, which Professor Schonbein, by a long- 
continued series of researches, has shown to result from a 
change in the oxygen of the air. He supposes that this sub- 
stance is composed of two atoms, which by their combina- 
tion partly neutralize each other, but which are separated 
by the repulsion of the electric spark, and when thus set free 
— have a much greater tendency to combine with other sub- 
stances than in their ordinary state of union. Oxygen thus 
changed or dissociated is called ozone, and as it would ap- 
pear, performs an important part in many of the molecular 
and chemical phenomena of the atmosphere. To this in- 
creased combining power of oxygen "may be attributed the 



-1859] WRITINGS OP JOSEPH HENRY. 345 

fonnation of the nitric acid we have mentioned, and with- 
out such an explanation, it would bo difficult to conceive 
how particles of oxygen and nitrogen, \Vhich are rendered 
mutually repulsive by the electrical discharge, should enter 
into chemical combination. 

We have seen that though metals are generally good con- 
ductors, yet when electricity falls upon a rod of iron or cop- 
per explosively, the energetic repulsion, which must always 
accompany these explosions, tends to throw the particles off 
on all sides, and when the discharge is sufficiently great 
the conductor itself is dissipated in vapor. Water is a much 
inferior conductor to iron, and though a large mass of it will 
silently discharge a conductor, yet it offers great resistance 
to the transmission of electricity explosively, and hence the 
electricity is sometimes seen to leave a conductor, and pass 
a considerable distance over the surface of water, rather than 
to force its passage through the interior of the mass. It is 
therefore highly important in arranging lightning rods that 
they should be connected at the lower end with a large sur- 
face of conducting matter, to prevent as far as possible the 
fluid from leaving the rod in the case of an explosive dis- 
charge. 

Electricity of the Atmosphere, 

Having given in the preceding sections a brief exposition 
of the general principles of electricity, we are now prepared 
to apply these to an exposition of the phenomena of atmos- 
pheric electricity. 

The origin of the electricity of the atmosphere has long 
occupied the attention of physicists, and at different times 
they have apparently settled down on some plausible hypoth- 
esis which merely offered a probable explanation of the 
phenomena without leading to new facts or pointing out 
new lines of research. 

The earth, as is now well known, is an excellent con- 
ductor for the most feeble currents of electricity, provided 
the contact with it of the electrified body be sufficiently 
broad. The aerial covering which surrounds it, is however 



346 WRITINGS OF JOSEPH HENRY. [185S- 

a non-conductor, and is capable of confining electricity in 
a condition of accumulation or of diminution, and of pre- 
venting the restoration of the equilibrium that without the 
existence of this insulator, would otherwise take place. 

The hypothesis was at first advanced that the earth at- 
tracts thesetherial medium of celestial space and condenses 
it in a hollow stratum around the whole globe; that the 
electricity of the atmosphere is due to the action of this 
exterior envelope. Dr. Hare, our countryman, has presented 
this hypothesis with considerable distinctness. Without 
denying the possibility or even probability of such a distri- 
bution of electrical excitement, we may observe that if this 
electrical shell were of uniform thickness, and we see no 
reason to suppose it should vary in different parts in this re- 
spect, it would follow from the law of central forces, that it 
could have no effect in disturbing the equilibrium on the 
surface or in the interior of the earth ; a particle of matter 
remaining, as we have seen, at rest or un-affected at any 
point wittiin a hollow sphere. This fact appears to militate 
against the truth of this assumption. 

Another hypothesis attributed the electricity of the at- 
mosphere to the friction of the winds on each other and on 
the surface of the earth, but careful experiments have shown 
that the friction of dry air on air, or of air on solids or 
liquids does not develop electrical phenomena. 

The next hypothesis — advanced by Pouillet, referred 
the electricity of the atmosphere to the evaporation of 
water, particularly that containing saline ingredients. But 
when pure water is carefully evaporated in a space not ex- 
posed to the sky, no electricity is produced except by the 
friction with the sides of the vessel in the act of rapid ebulli- 
tion; and when the experiment is made with salt water the 
electrical effects observed are found to be produced by an 
analogous friction of the salt against the interior of the ves- 
sel. When pure water is evaporated under a clear sky the 
vapor produced is negativel)' electrified; but this state is 
contrary to that in wliich the atmosptiere is habitually 
found. 



348 WRITINGS OP JOSEPH HENRY. [1855- 

of the whole subject, we have been obliged to reject them 
all as insufficient, and compelled in the present state of 
science to adopt the only conclusion which appears to oflfer 
a logical explanation of all the phenomena, namely that of 
Peltier, which refers them not to the excitement of the air, 
but to the inductive action of the earth primarily electrified- 

The author of this theory we are sorry to say did not re- 
ceive that attention which his merits demanded, nor his 
theory that consideration to which so logical and so fruitful 
a generalization was justly entitled. Arago, in his great 
work on the phenomena of atmospheric electricity, does not 
allude to the labors of Peltier; the reason of which may 
be that his work yvas not intended as a scientific exposition 
of the principles of the phenomena, but merely a collection 
and classification of observed facts. 

Peltier commenced the cultivation of science late in life 
and since the untutored mind of the individual, like that 
of the race, passes through a series of obscure and complex 
imaginings before it arrives at clear and definite conceptions 
of truth, it is not surprising tliat his first publications were 
of a character to command little attention, or rather to 
excite prejudice on account of their apparently indefinite 
character and their want of conformit}^ with established prin- 
ciples. His theory of atmospheric electricity requires to be 
translated into the ordinary language of science before it can 
be readily comprehended even by those best acquainted with 
the subject, and hence his want of appreciation may be at- 
tributed more to the peculiarities of the individual than to 
the fault of the directors of science in France. 

According to the theory of Peltier, the electrical phenom- 
ena of the atmosphere are entirely due to the induction of 
the earth, which is constantly negative or what in the theory 
of Du Fay is called resinous. He offers no explanation (so 
far as we know) of this condition of the earth, which at first 
sight would appear startling, but on a little reflection is not 
found wanting in analogy to support it. The earth is a 
great magnet, and possesses magnetic polarity in some 
respects similar to that which is exhibited in the case of 



-1859] WRITINGS OF JOSEPH HENRY. 349 

an ordinary loadstone or artificial magnet. This magnetism 
is of an unstable character however, and is subjected to 
variations in the intensity and in the direction of its polar 
force. In like manner we may consider the earth as an im- 
mense prime conductor negatively charged with electricity, 
though its condition in this respect may — like that of its 
magnetical state — be subject to local variations of intensity, 
and perhaps to general as well as partial disturbance. 

It may be said that this merely removes the difficulty of the 
origin of the electricity of the atmosphere to an un-explained 
cosmical condition of the earth ; but even this must be con- 
sidered an important step in the progress of scientific inves- 
tigation. The hypothesis of Peltier has since his death been 
rendered still more probable by the labors of Sabin, Lloyd, 
Lament, Bache, and others, in regard to certain perturba- 
tions of the magnetism of the earth, which are clearly refer- 
able to the sun and the moon. It must now be admitted 
that magnetism is not confined to our earth, but is common 
to other — ^and probably to all the bodies of our system ; and 
from analogy we may also infer that electricity, a co- 
ordinate principle, is also cosmical in its presence and 
the extent of its operation. That the earth is neg- 
atively electrified was proved by Volta at the close of the 
last century. For this purpose he received the spray from 
a cascade on the balls of a sensitive electroscope ; the leaves 
diverged with negative electricity. 

This experiment has been repeated in various parts of the 
globe, and always^ with the same result. That it indicates 
the negative condition of the earth is evident, when we re- 
flect that the upper level from which the water falls must 
be considered as the exterior of the charged globe, and hence 
must be more intensely electrified than points nearer the 
centre. Since the earth is (as a whole) a good conductor of 
electricity, as shown by the operations of the telegraph, the 
electrical tension of it cannot differ much in different parts, 
and we are at present un-acquainted with any chemical, 
thermal, or mechanical action on land of sufficient magni- 
tude to produce this constant electrical state. We are there- 



350 WRITINQS OF JOSEPH HENRT. [1855- 

fore induced to adopt the conclusion that the earth — in rela- 
tion to space around it, is permanently electrical; that perhaps 
the setherial medium, which has been assumed as the basis 
of electricity, as was supposed by Newton, becomes rarer in 
the vicinity of — and within bodies of ponderable matter. Be 
this as it may, all the phenomena observed in the atmos- 
phere, and which have so long perplexed the physicist, can 
be apparently reduced to order, and their dependencies 
and associations readily understood, in accordance with the 
foregoing assumption. This is not a mere vague supposi- 
tion, serving to explain in a loose way certain phenomena, 
but one that enables us not only to group at once a large 
class of facts, (which from any other point of view, would 
appear to have no connection with each other,) but also to 
devise means for estimating the relative intensity of action, 
and to predict both in mode and measure changes of atmos- 
pheric electricity before they occur. It follows, as a logical 
consequence from this theory, that salient points, such as 
the tops of mountains, trees, spires, and even vapors, if of 
conducting materials, will be more highly excited than the 
general surface of the globe, in a manner precisely similar 
to the more intense excitement of electricity at the summit 
of a point projecting from the surface of the prime conductor 
of an ordinary electrical machine. 

It also follows from the same principle that if a long 
metallic conductor be insulated in the atmosphere, its lower 
end, next the earth, will be positive, and the upper end nega- 
tive. The natural electricity will be drawn down by the un- 
saturated matter of the earth into the lower end of the wire, 
which will there become redundant, while the upper end 
will be rendered negative or under-saturated. That this 
condition really takes place in the atmosphere was proved 
in a striking manner by the experiment of Gay-Lussac and 
Biot in their celebrated aerial voyage, which consisted in 
lowering from the balloon an insulated copper wire, termi- 
nated at each end by a small ball. The upper end of this 
was found to be negative, and consequently the lower end 
must have been positive, since the whole apparatus — ^includ- 



-1809] WBITINOS OF JOSEPH HENBY. 851 

ing the balloon — was insulated. The experiments should bo 
iq>eated at different elevations by some of our modern 
aeronauts, since the results obtained would have an impor- 
tant bearing on the theory of atmospheric electricity. 

The same results may be shown in a simpler manner by 
the method invented by Saussure. This consists in attaching 
aleaden ball/, (Fig. 12,) to a long wire covered with silk or var- 
nish, connected by means of a slight spring to the hook of 
an electroscope. When this bulb is 
thrown upward by means of a string 
and handle p, so as to rise to a con- 
siderable lieight in the air, the pith 
haWsgg, of the electroscope diverge 
with positive electricity, and the 
wire is dis-connected from the in- 
strument That this effect is not due 
to the friction of the bulb and the air 
is shown by whirling it in a hori- 
zontal circle round the head; not 
m' the least sign of electricity in this 
case being exhibited: and that it 
"°" "■ is not charged by absorbing free 

electricity from the air, is proved by the fact that when 
the ball is thrown horizontally no excitement is manifest. 
The result is however just such as would be produced by the 
induction of the earth acting on the natural electricity of the 
wire and drawing it down to its lower extremity. A pre- 
cisely similar effect would also be produced if the upper 
surface of the atmosphere were charged with this electricity. 
The intensity of the charge which the electroscope receives 
will depend upon the elevation to which the ball ascends, or 
in other words on the perpendicular component of the direc- 
tion of the wire. 

The method employed by Saussure in observing the varia- 
tions of the electricity of the atmosphere illustrates the same 
principle. For this purpose he made use of one of his own 
electroscopes such as shown in Fig. 12, It consists of a 
bell-glass with a brass stem, d e, surrounded with sealing- 
wax, and two small pith balls, g g, suspended by very 




352 WRITINGS OF JOSEPH HENRY. [1855- 

fiDe wires: cb is & metallic foot, and h k slips of tin-foil 
pasted on the inside and outside of the glass to discharge 
the pith balls when the electricity is 
so strong as to cause them to strike the 
glass. To measure the electrical in- 
tensity with this instrument the hook 
a was removed, and its place supplied 
with a pointed brass rod. The elec- 
troscope was first brought in contact 





FiQ. 13, Fio. u. 

with the ground as exhibited in Fig. 13; then held vertically 
ns shown in Fig. 14, and gradually elevated until the leaves 
begun to diverge. Saussuro found that the height to which 
the instrument was required to be elevated before the leaves 
showed signs of electricity varied at different times, and he 
estimated the intensity of the electricity of the atmosphere 
by the inverse ratio of this height. 

The esplaDation 
of this will be read- 
ily seen by a refer- 
ence to Fig. 15, in 
which C, D, repre- 
sents a portion of 
the surface of the 
earth negatively 
charged, and abc,a, 
perpendicular con- 
^~ ductor terminated 
above and below 
by a bulb. In tbig 



iSi*Sl«i 



18591 WRITINGS OF JOSEPH HENRY. 353 

condition the un-saturated matter in C, D will act upon 
each atom of the fluid in the conductor, and tend to draw 
the whole down into the lower bulb; the atoms at a will not 
only be attracted downward by the action of the earth on 
itself, but also pressed downward by the attraction of the 
earth on all the atoms above it, and hence the intensity of 
the electricity of the lower part of the conductor will be in- 
creased by an increase in the perpendicular length of the 
rod. Now, if we connect the lower bulb of the rod with the 
earth by means of a good conductor, the redundant electricity 
of the lower end will be drawn off into the earth and will 
no longer re-act by its repulsion on the electricity of the rod 
to drive it back into the upper bulb, and hence this will 
become intensely negative, and in this condition it will be 
a salient point on the surface of the earth. If while the 
apparatus is in this condition wo could touch the upper ball 
with an electroscope it would exhibit a negative charge. 

If a conductor 20 feet in length were made to revolve on 
a horizontal axis, passing through the middle of its length 
80 that it could be immediately changed from a horizontal 
to a vertical position, any change in the apparent condition 
of the atmosphere would be shown by the greater or less in- 
tensity of the balls, as in succession they passed the lower 
point of their circuit ; and an apparatus in the form of radia- 
ting conductors like the spokes of a wheel, if made to revolve, 
would furnish a constant source of electricity. An apparatus 
of this kind was constructed b)' M. Palmieri, of Italy, and 
might be used perhaps with success in studying the condi- 
tion of the atmosphere in ascensions. 

The most convenient apparatus however for exhibiting 
electricity by the induction of the earth is that invented by 
M. Dellman, and shown in Fig. IG; which consists of a 
large brass ball a supported on a thick brass stem — held 
insulated inside of a glass tube by passing througli corks of 
gum shellac. The apparatus is fastened to a pole whicti is 
temporarily elevated into the air by a windlass or the hand, 
on the top of a house. When it reaches the height intended, 
the wire k, connected with the earth below, is pulled, the end 
2a-2 



WBITIKGS OF JOSEPH HENRY. 



[1SS5- 




of the bent metallic lever g h, is depressed, and 
the fork t brought into contact with the stem 
of the globe, and thus a perfect metallic con- 
nection is formed between the latter and the 
ground. The wire k is then released, the lever 
falls back, the hall is insulated from the earth, 
brought down, and applied to an electroscope, 
and in all cases, when the sky is clear, is found 
to be negatively electrified. If the wire k he 
insulated through its entire length, and termi- 
nated in a bulb at a little distance from the 
earth, and a pull be given to It by means of a 
rod of glass, at the instant of contact of the 
point i with the stem d, the tower bulb will ex- 
hibit a positive charge of electricity. The ar- 
rangement will, in fact, be precisely the same 
as that exhibited in the previous figure, (Fig. 
15), namely, a vertical conductor, the upper 
ii-io. 10. pn^ of which is rendered mintis and the 
lower end plus by the induction of the earth. This effect 
is entirely due to induction, and is independent of any free 
electricity which may exist in the air. The results are ex- 
hibited with the greatest intensity during perfectly clear and 
dry weather; and arc not observed when the conductor is 
placed horizontally, but the indications increase as its upper 
end is gradually brought nearer the perpendicular. 

That these effects are not due to the free electricity of the 
atmosphere is satisfactorily shown by the original experi- 
ments of Peltier. For measuring the intensify of the in- 
ductive influence of the earth he made use of an electrometer 
represented in Fig. 17; in which a A, is a glass cylinder fur- 
nished with a wooden foot and a glass cover : through the cen- 
tre of this is cemented a brass tube carrying a ball c at the 
top, and an arched straddling wire at the bottom. At the 
level of the foot of the arched wire is suspended a fine 
magnetized needle g, the height of which is adjusted by 
the screw It. The intensity of the electricity is measured by 
the divisions pointed out by the deflected needle on the slip 



WRITINGS OF JOSEPH HENRY. 



355 




of paper surrounding 
the cylinder. This in- 
strument, which is 
very sensitive, has 
been modified and im- 
proved by Dellman. 

On the top of the 
flat roof of his house 
Peltier phiced a flight 
of steps by which he 
could ascend holding 
in liis hand an ordi- 
nary gold-leaf electro- 
scope armed with a 
^ comparatively largo 
^' sized polished ball. 
■ The ball of the elec- 
troscope was held at 
the height say of four 
feet above the roof of 
the house, and in this position it was touched by the end 
of a wire connected with the earth below. It thus formed 
the termination of a perpendicular conductor, and was 
of course n^atively electrified — the bulb more intensely 
than the leaves below, but the stratum of air in which it was 
placed being in the same state it exhibited no signs of elec- 
tricity. It was then elevated by ascending the steps to the 
height of six feet above, and held by the lower plate. The 
loaves in this case diverged with negative electricity, because 
the ball was still farther removed from the earth, and the 
attraction being lessened, the part of the electricity in the 
leaves was set free and ascended to the bulb by repulsion, 
leaving a deficiency in the leaves. When the electroscope 
was brought down to its first position the leaves again col- 
lapsed since there was again an equilibrium ; and when the 
electroscope was depressed below its normal position the 
leaves became positively electrified by the increased attrac- 
tion of the ecirth, and in this way the electroscope was 



Fio. 17. 



356 



WRITINGS OF JOSEPH HKXBY. 



[1855- 



made to diverge, to converge, and diverge again, by simply 
changing its elevation. 




Fig. la 

Fig IS is intended to illustrate the condition of the elec- 
troscope in the three positions in which it is supposed to be 
supported on three metallic conductors of diflferent heights. 
The electroscope brought into neutral condition by the ball 
is shown in the middle of the figure at B, in which the con- 
nection of the rod with the ball is indicated by the dotted line. 
When the electroscope is raised by the hand to a higher ele- 
vation its condition is exhibited by C, in which the greater 
height of the rod causes a greater amount of electricity to bo 
drawn down, and the top of the rod and the bottom of the 
electroscope in connection with it to become more intensely 
negative, and hence to draw down into the leaves a portion of 
tlie natural electricity of the ball, and cause the former to di- 
verge with positive excitement relative to the air around. 

The condition of the electroscope when brought to a lower 
level is illustrated by A/m which the shortening of the con- 
ductor reduces the number of atoms on which the electricity 
of the earth acts, and hence those at the top are more pressed 
upward by their self-repulsion than in the former case, con- 



~I85d] WRITINGS OF JOSEPn HENRY. 357 

sequently a portion of the natural electricity is driven into 
the upper ball and the leaves themselves diverge with a 
negative charge: the condition being opposite to that shown 
at C. The writer had the pleasure in 1837 of witnessing this 
interesting experiment as performed on a dry clear day by 
Peltier himself - 

In order that the result may be shown with a slight change 
of elevation it is necessary that a large ball be employed, so 
that the efiect may be multiplied by all the electricity of the 
greater surface. When the electroscope is terminated with 
the point of a fine needle, (though this is the best means of 
attracting electricity from the air at a distance,) no efiect 
will be exhibited, provided the weather is dry and the sky 
cloudless. 

From these experiments it appears evident that the 
positive electricity with which the air is apparently always 
charged in dry and clear weather, is not due to the free elec- 
tricity of the atmosphere, but to the induction of the earth 
on the conducting materials of which the instruments are 
in whole or in part composed. 

It is not diflficult to deduce from the same general princi- 
ples the apparent changes in the electrical state of the atmos- 
phere at difierent times of the day and in difierent hygro- 
metrical conditions of the air. Vapor of water mingled with 
the atmosphere renders the latter a positive conductor; and 
when the moisture of the air extends up as high as the upper 
part of the apparatus in Fig. 16, feeble negative electricity 
will by slow conduction be difi*used through the adjacent 
strata, which acting upon the ball a will lessen the effect of 
the more intense action of the earth. While the latter 
tends to draw the natural electricity of the conductor down 
into its lower part^ and to render the upper end negative, 
the vapor around the ball will tend to draw it slightly up- 
ward and thus diminish the effect, and lead the casual 
observer to suppose that the air is less positively electrified. 
Peltier in this way has shown (as well as Quetelet and Dell- 
man) that the variations of the electricity of the atmosphere 
observed from day to day, and at different times in the 



358 WniTINGS OF JOSEPH henry. [1855- 

twenty-four hours, correspond inversely with the variations 
in the amount of vapor. 

The experiments we have thus far described are intended 
to establish the inductive character of the atmosphere in its 
condition of dryness and serenity, particularly during clear 
and cold weather. 

We have employed movable conductors terminated by 
balls which have been of the most favorable form and rela- 
tive dimensions to exhibit the effects of induction. The 
apparatus usually employed before' the experiments of 
Peltier, were princijially stationary insulated conductors 
terminated by f>oiuts o.bove, which as we have seen act 
powerfully in discharging electricity from a body, or in ab- 
sorbing it from the surrounding medium. 

If in the experiments with the apparatus, Fig. 16, the rod 
be terminated by a point instead of a ball, but feeble excita- 
tion will be observed during clear, cold weather, because 
the f>oint exhibits so exceedingly small a surface that but 
verv little electricitv can be drawn down into the lower end 
before the intensity of attraction of unsaturated matter up- 
wards comes into an equilibrium with the attraction of the 
earth dowuwai-ds. With this instrument the observer would 
probably make a record to the effect that the electricity of 
tlie atmosphere was very feeble, whereas if the experiment 
were made with the apparatus previously described an 
opposite condition would be noted. But the result would 
be entirely different if the air were damp, and the insulated 
rod elovate<l to a considerable height: the negative intensity 
of the upper end would be suflicient to attract a portion of 
the natural electricity from the surrounding medium, even 
although this had become slightly negiitive by the previous 
induction of the earth. In this case the pointed conductor 
would indicate a large amount of electricity. 

The iutonsity of the induction may even become so great 
as to absorb a portion of the natural electricity of the dry 
atmosphere as in the case of a very long wire, the upper end 
of which is furnished with a series of points, and raised to a 
gi-eat height by means of a kite. The points may attract 



\ 



„„..,»"""■ 



[185»- 







-18591 WRITINGS OF JOSEPH HENRY. 361 

It is asserted by Mr. Wise that the thunder-cloud, when 
viewed on one side from a sufl5cient elevation, presents the 
appearance of an hour-glass, the upper and the lower ends 
spreading out almost into two distinct clouds, as seen in 
Figure 19. 

We find that the same form of the thunder cloud has been 
described by other aerial voyagers, also by Volta ; and we 
are inclined to consider it the usual one presented by this 
meteor, since it is precisely that which would be produced 
by the self-repulsion of the upper and lower parts of the 
cloud, each charged as it is throughout its mass with the 
same kind of electricity. The middle of the perpendicular 
dimensions of the cloud as illustrated by the perpendicular 
conductor, Figure 15, will be neutral, and hence no tendency 
to bulge out at this point will exist. Mr. Wise also states 
tliat flashes of sheet lightning are constantly seen at c, in the 
middle space; and sometimes intense discharges from the 
upper to the lower part of the cloud; — appearances in exact 
conformity with the views here presented. 

The immense number of discharges of lightning from a 
single thunder-cloud in its passage over the earth, through 
a distance in some cases of more than 500 miles, indicates a 
constant supply of electricity ; and this is found in the con- 
tinued rusjiing up of new portions of moist air, and in the 
successive renewals of the perpendicular column with fresh 
materials, the electrical equilibrium of which is disturbed 
by induction. 

In the case of a tornado or water-spout, the ascending cur- 
rent of air is confined to a very slender column, in which 
the action is exceedingly intense; and since it is scarcely 
possible that the rushing in from all directions of the air 
below to supply the upward spout can be directed to pre- 
cisely the same central point, a whirling motion must be 
produced. This will tend to limit the diameter of the spout, 
and to create a partial vacuum at the axis of the column, in 
which the moist air will have its vapor condensed by the 
cold of the sudden expansion, arid a conductor will thus be 
formed extending from the cloud to the earth. Through 



362 WRITINGS OP JOSEPH HENRY. [1855- 

this conductor a constant convectivo discharge of electricity 
will take place, and all the phenomena described by Dr. 
Hare will be exhibited. 

In this view of the nature of the tornado or water-spout, 
although we adopt with Franklin and Espy, as the character- 
istic of the commotion of the atmosphere, the rushing up- 
ward in the form of a column (on the principles of hydro- 
statics) of a stratum of heated and moist air which had ac- 
cumulated at the surface of the ground, yet the phenomena 
are modified and increased in number by the great amount 
of electricity which must be evolved by the simple action of 
the continued elevation of new portions of a constant stream 
of moist air. Since the conductor in the case of the tornado 
or water-spout, extends downward near to the earth, and 
the discharge is continually taking place, the cloud which is 
spread out immediately above will be negatively electrified, 
and the upper jx^rtion of the cloud, as exhibited in Figure 
19, will be wanting. The greater or less degree of conduc- 
tion of the depending spout will vary the phenomena and 
give rise to the different appearances which have been seen 
at the surface of the water. When the conductor does not 
quite reach to the earth visible discharges of electricity will 
be exhibited, and the surface of water will be attracted up- 
ward. When the conducting material of the spout touches 
the surface of the water, the liquid will be depressed. 

That the rushing up of the air with intense violence does 
take place in the column of a land or water-spout is abund- 
antly proved by direct observation, and that electricity can- 
not be the cause of this action, but is itself an effect, is 
proved by the fact, that since the column of moist air ex- 
tends to the earth, discharges of the fluid must be made 
through it which would soon exhaust the cloud, were it not 
constantly renewed. In some instances the meteor has been 
known to continue its destructive violence along a narrow 
line of more than two hundred miles in length. To merely 
refer this prolonged action to a. whirling motion of the air, 
without attempting to explain on known principles of science, 
the renewed energy of the rotation, is to rest satisfied with 
a very partial anlysis of the phenomenon. 



-1859] WRITINGS OP JOSEPH HENRY. 363 

If by the action of an elevated horizontal current of air 
the upper part of a thunder-cloud be separated from the lower, 
we shall have a mass of vapor charged entirely with negative 
electricity, and from such a mass floating high in the atmos- 
phere a new evaporation may take place by the heat absorbed 
directly from the sun. (Shown at d, Fig. 19.) The column 
of invisible vapor thus produced being a partial conductor 
elongated upward, the attraction of the earth will draw down 
a new portion of its natural electricity into the cloud from 
which the vapor was produced, and thus diminish its negative 
intensity. If now the upper end of this transparent column 
be condensed by the cold of the greater altitude into visible 
vapor, it will form a cloud of the second order of negative 
intensity. We shall thus have according to Peltier lower 
clouds intensely excited with positive electricity, clouds of 
medium elevation either neutral or slightly negative, and 
the highest cirrus clouds, which are formed by the secondary 
evaporation we have mentioned, strongly excited with nega- 
tive electricity. 

Since particles of ponderable matter similarly electrified 
repel each other, it is evident that the electrical state ©f the 
cloud must in some degree counteract the tendency to con- 
densation which would result from the cold of the upper 
regions; and also the same action in the lower clouds will 
tend to prevent precipitation in the form of rain, even 
though the atoms of vapor are in a condition to coalesce into 
drops of water. It is evident also since the earth is nega- 
tively electrified, that the particles of vapor in the same 
state will be repelled farther from the surface, and those 
which are positively electrified will be drawn down. Hence, 
the negative clouds will tend to retain their elevated posi- 
tion, although they may be pressed downward by descend- 
ing currents. 

Negative clouds may also be formed near the surface of 
the earth by a detached portion of cloudy matter under a 
cloud more highly charged with positive electricity, which 
will cause the former by induction to discharge its positive 
electricity into the earth as well as a portion of its natural 



364 WRITINGS OF JOSEPH HENRY. [1855- 

electricity ; and if the upper cload bo afterward driven 
away by the wind, the lower will be left highly negative. 

Peltier states that he can determine from the appearance 
of a cloud whether it be positively or n^atively charged. 
Clouds negatively electrified, (according to him,) are of a 
bluish gray color, while those which are positively charged 
are white and exhibit at the setting sun a red appearance. 

From the foregoing considerations it must be evident that 
in addition to the disturbance which is produced in the atmos- 
phere by the variations of heat and moisture we must take 
into account those that result from the changes in the electri- 
cal condition of the atoms of moisture. Though they may 
not be as important as the former, still they must modify the 
conditions of the general phenomena, and no theory of 
storms can be complete which does not include the effect 
of this agent. 

On the principles we have developed, the discharges of 
lightninj^ which are exhibited in volcanic eruptions are 
readily understood. The column of aqueous vapor, heated 
air, and other conducting materials, which sometimes rises to 
a great elevation from Vesuvius, must be subjected to the 
inductive action of the earth, and consequently the elec- 
tricity of the upper end of the column, as soon as its ele- 
vation is sufficient to produce a condensation of the vapor, 
by the cold of the higher regions, must send down to the 
lower part of the column a large amount of electricity which 
when the length is great and the ascending stream rapid, 
will manifest itself in discharges of lightning. 

In accordance with the same principles, thunder-storms 
have been artificially produced in a peculiar state of the 
atnia^phere. About thirty yeai-s ago a farmer at Greenbush, 
near Albany, collected on a knoll in the middle of a field 
a lariro amount of brushwood, which was set on fire simul- 
tiuuxnisly at different points, and, burning, gave rise to an 
ivsconding column of heated air, extending to a great alti- 
tude. The air rushing in to supply the upward current as- 
sumed a rapid rotary motion, accompanied by a loud roar- 
in«' antl discharges of lightning of sufficient magnitude to 



-1859] WRITINGS OF JOSEPH HENRY. 365 

frighten the laborers from the field. The explanation in 
this case is too obvious to require a formal statement. 

In the equatorial regions under a vertical sun masses of 
moist air are constantly rising during the daj'time and pro- 
ducing electrical discharges to the earth. The vapor there- 
fore which accompanies the reverse trade winds in the upper 
region must be negatively electrified, while the earth in the 
torrid zone must constantly be receiving electricity from the 
clouds. From this we may infer that there is a current of 
electricity through the earth, from the equator towards the 
poles and a neutralization by means of the air above, which 
may give rise to the aurora polaris. 

Arago has described the different forms of lightning under 
three classes. The first class comprises the lightning which 
consists of a vivid luminous line or furrow, very narrow and 
sharply defined, the course of which is not a direct line, but 
is that denominated zig-zag. This peculiar form of light- 
ning according to Moncel is referable to the effect of partial, 
interrupted conduction, and may be imitated.by sprinkling 
iron filings on a plate of glass; the bifurcations of the dis- 
charge may also be referred to the same cause. The drops 
of rain distributed through the air perform the office of the 
particles of iron filings in the experiment, the repulsion 
of the electricity tending to separate it into different streams. 

The next class consists of what is called "sheet light- 
ning," which instead of being narrowed to bright sinuous 
lines, appears on the contrary to extend over immense sur- 
faces. It not unfrequently has an intensely red tinge and 
sometimes a blue or violet color predominates. The color 
probably belongs to the flashes of lightning which take place 
at a great elevation, and seem to illuminate lower clouds, 
and thus to present the appearance of a broad flash. 

We may also mention that flashes of lightning are some- 
times observed in a summer evening without thunder, and 
known as "heat lightning." They are however merely the 
light from discharges of electricity from an ordinary thunder- 
cloud beneath the horizon of the observer, reflected from 
clouds, or perhaps from the air itself, as in the case of 



366 WRITINGS OP JOSEPH HENRY. [1855- 

twilight. Mr. Brooks, one of the directors of the telegraph 
line between Pittsburg and Philadelphia, informs us that on 
one occasion to satisfy himself on this point he asked for 
information from a distant operator during the appearance 
of flashes of this kind in the distant horizon, and learned that 
they proceeded from a thunder-storm then raging two hun- 
dred and fifty miles eastward of his place of observation. 

The third class is called "globular lightning," which is re- 
markable (besides its peculiarity of form) for the slowness of 
its motion. The occurrence of this form of lightning is very 
rare, and were not the phenomenon well authenticated, we 
should be inclined to regard it as a delusion. But it does not 
comport with the cautious procedure of true science to deny 
the existence of all appearances which may not come within 
the prevision of what are considered as established princi- 
ples. Although when facts of an extraordinary nature are 
related to us, they should not be received with that easy cre- 
dence which might be due to less remarkable phenomena, yet 
after having fully satisfied ourselves of their reality, we must 
endeavor to collect all the facts connected with them, and to 
ascertain with accuracy the essential conditions on which 
they depend. Arago has given a number of instances of 
this remarkable form of the electrical discharge, the general 
appearance of which is that of a ball moving slowly through 
the air and sometimes when coming near a body, exploding 
with tremendous violence. 

The only explanation which has been suggested for this 
remarkable meteor, and which at first sight appears to be- 
long entirely to some other class of phenomena than those 
denominated electrical, is that which was in part suggested 
(I believe) by Sir W. Snow Harris. According to his hypoth- 
esis, the ball of light is the result of what is analogous to that 
which is known as a glow discharge, a phenomenon familiar 
to all who are in the habit of making electrical experiments. 
When a conductor connected with the earth is brought near 
a charged body, particularly when the air is damp, a partial 
silent discharge will take place, during which (although 
there may be no light perceptible in the space between the 



368 WRITINGS OP JOSEPH HENRY. [1855- 

although it must have been at the time many miles in alti- 
tude above the surface of the earth. 

Iiuiudive adion of the doud. — A cloud formed as we have 
described must produce a great inductive effect on the earth 
beneath, and as it is borne along (from the west in this lati- 
tude) over the ground, the intensity of the electricity of the 
lower part must constantly vary, on account of the differing 
conductive capacity of the materials at or below the sur- 
face. For example, since water is a better conductor than 
dry earth, if the cloud is moving in a line that prolonged 
would cross a river, its course will frequently be changed, and 
in a similar way we can explain the fact that discharges of 
lightning more frequently fall on some places than others. 
Although the cloud may be impelled in the same direction 
by the wind, yet the attraction of the surface of the water 
(rendered more than naturally negative by induction,) will 
tend to draw it from its course. And since the induction 
acts at a distance through all substances, if a quantity of 
water or good conducting material exist below the surface of 
the earth, the cloud will be similarly affected. It frequently 
happens that when a heavy discharge of liglitning passes 
near a house or descends along a rod, inductive effects are 
exhibited which are more startling than dangerous. 

We have seen in the experiment described on page 693 (Fig. 
9,) that an induced spark was exhibited at the edge of a' large 
disc covered with tinfoil, in the lower story, by suddenly 
drawing the electricity from a similar disc in the upper part 
of a house. A precisely similar arrangement, but on a much 
more gigantic scale, is presented when a highly charged 
thunder-cloud is in the zenith of a building. Now if the 
intensity of this be suddenly diminished by a discharge to 
the earth, flashes of electricity and sparks from different ob- 
jects within the house will be observed. The explanation 
of this is very easy. The free electricity of the cloud, which 
we may suppose to be positive, repels all the positive elec- 
tricity of conductors and partial conductors into the ground, 
and renders them negative. They will be brought into this 
state very gradually however, either by the comparatively 



-1859] 



WRITINGS OP JOSEPH HENRY. 



slow approach of the cloud, or by its increase in intensity. _ 
The fluid therefore will escape into the ground withont being ' 
perceptible in the form of sparks, but when the repulsion is 
suddenly relieved, at least in part, by a discharge of the cloud, 
the natural electricity rushes back and exhibits itself in 
flashes and sparks, and may oven give shocks to persons in 
the vicinity. Although this sudden return of the electricity 
from the earth into which it has been driven, (in ordinary 
cases of conductors in a house supported by bad conducting 
materials,) is usually attended with but slight effects, yet it 
may under certain circumstances produce serious accidents^ 
particularly when a person is in good conducting eonnec- 
tiou with the earth. A remarkable instance of this kind was 
described by Mr. Brydone, in a letter to the president of the 
Royal Society, in 1787. 

Two laborers, each driving a cart loaded with coal, and 
sitting upon the front part, ascending a slightemiucnce, the 
one following the other at a distance of about twenty-four 
yards, as represented at M and L, Fig. 20, were conversing 




Fio. 20. 

about the thunder which was heard at a distance, when in 
aa instant the man in the hinder cart was astounded by a 



370 WRITINGS OP JOSEPH HENRY. [1855- 

loud report, and saw his companion and the two horses 
which he was driving fall to the ground. He immediately 
ran to his assistance, but found him quite dead. The horses 
were also killed, and appeared to have died without a struggle. 
The hinder cartman had the horses and driver of the forward 
cart full in view when they fell to the ground, but he saw 
no flash or appearance of fire, and was sensible of no shock 
or uncommon sensation. Each wheel was marked with a 
bluish spot on the tire, as if the iron had been subjected at 
that place to an intense heat, and directly under these spots 
were two holes in the ground, from which the earth was re- 
moved as if by an upward explosion. Flashes of lightning 
had been seen and thunder heard by Mr. Brydone also, who 
was in the vicinity at the time, but these were at the distance 
of five or six miles, as shown by the time elapsed between 
seeing the flash and hearing the thunder. There were no 
marks however of the exit of the discharge upwards from 
the body of the man or of the horses, or any efiect which 
could be attributed to a discharge immediately from the 
cloud. The accident was seen by another person, from a 
greater distance, who was also astounded by the loud report, 
saw the horses and man fall to the ground, and perceived 
the dust arise at the place, although he observed no lightning 
or fire at the time. A shepherd in a neighboring field, during 
the same storm, observed a lamb drop down dead, and felt at 
the same time as if fire had passed over his face, although 
the lightning and clap of thunder were at a great distance 
from him. This happened a quarter of an hour before the 
accident to the cartman, and not over three hundred yards 
from the same spot. A woman making hay near the bank 
of the river close by, fell suddenly to the ground, and ex- 
claimed to her companions that she had received a violent 
blow on her foot, and could not imagine whence it came. 

A scientific analysis of these phenomena is given by 
Earl Stanhope, on principles similar to those of induc- 
tion, which we shall translate into the precise language of 
that theory. Let us suppose a cloud eight or ten miles in 
length to be extended over the earth in the situation repre- 



-1859] WRITINGS OF JOSEPH HENRY. 371 

sented hy A B Cin Fig. 20, and let another cloud D E Fhe 
situated between the above-mentioned cloud and the earth. 
Let the two clouds be supposed to be charged with the same 
kind of electricity, and both positive. Let us further sup- 
pose that the lower cloud D E F he only so far from the 
earth as to be just beyond the striking distance, and the 
man, cart, and horses to be at L, under the part E of the 
cloud which is nearest the earth. Now let the remote end 
C of the upper cloud approach the earth within striking dis- 
tance, and suddenly discharge itself at G. The efifect which 
would be produced by this arrangement, at the moment of the 
discharge Cc 0, will be understood by considering the condi- 
tion of the electricity in the two clouds, and in the earth a 
moment previous to the discharge. Both clouds being posi- 
tive, the two will act upon each other by repulsion, the free 
electricity of the lower cloud will be driven down into its 
lower surface, and will be accumulated particularly in the 
point E nearest to the earth. The ground underneath the 
lower cloud,. and more especially at L, where the distance is 
least, will become highly negative. The natural electricity 
will be driven down into the ground by repulsion, and will 
be retained there as long as this condition remains, but when 
a discharge takes place at the point C G, if the cloud Bhea 
good conductor, the repulsion at A and D will be suddenly 
removed, and the natural electricity of the earth will return 
with a rush to the surface and pass beyond its [)oint of 
natural equilibrium, as in this case into the man and horses. 
The loud report was caused by the discharge from Z) to 4, 
which was invisible to the eye of the spectators on account 
of the density of the lower cloud. 

An experimental illustration of the effects produced in this 
case may be readily furnished by charging two conductors, 
arranged in the relative position of the two clouds. At the 
moment a spark is drawn from the end C a discharge is 
observed at D A. - The death of the lamb and the shock 
felt in the foot of the woman were both produced according 
to this view by the sudden rushing up of the natural elec- 
tricity of the ground, when the repulsion in the upper cloud 
was in part diminished by the distant discharge. 



372 WRITINGS OF JOSEPH HENRY. [1855- 

The inductive action at a distance which we have described 
affords a rational exposition of the effects which are per- 
ceived by persons of nervous sensibility on the approach of a 
thunder-storm, and may also be connected with the change 
which is said to take place suddenly in liquids in an un- 
stable condition, such as the souring of milk and other sub- 
stances near the point of fermentation. But whether the 
latter effects are due to the inductive action of the electricity 
or the tremor produced by the thunder, has not to our 
knowledge been definitely settled. If the effects are due to 
induction, it is probable that they would be greater in the 
case of milk in a metallic pan resting on the earth, than in 
one of glass, supported on glass legs or on a thick cake of 
bees-wax. 

Precautions with regard to lightning. — Men have often been 
struck by lightning in open plains, and since the human 
body is a good conductor of electricity, from the principles 
above stated it must be evident that when standing it 
would be more likely to be struck than any point on the 
earth in the vicinity. There is less danger in a horizontal 
position, particularly if the person be resting on some non- 
conducting substance which would prevent the natural elec- 
tricity from descending into the earth. Near the foot of a 
tall isolated tree is always considered a dangerous position, 
and this is in accordance not only with facts but well-estab- 
lished principles. The upper part of the tree being a par- 
tial conductor, particularly if covered with foliage, will be- 
come electrified by induction, will attract the discharge to 
itself, and in the passage of the lightning toward the earth 
it will act with energetic induction on all surrounding objects, 
and since the body of the man is a better conductor than 
the wood, the instantaneous inductive effect of the de- 
scending bolt will be greater on the head of a man than 
on the remaining part of the tree, and hence it will 
diverge from the line it was pursuing, break through the 
air, and pass through the body of the man. To attempt 
to explain this phenomenon by merely saying that the elec- 
tricity leaves the tree because the human body is a better 



-1859] WRITINGS OF JOSEPH HENRY. 373 

conductor than the wood is to attribute to this agent pre- 
science and forethought, but by an application of the prin- 
ciples of induction, the whole is referred to the simple action 
of attraction and repulsion. In the interior of a house the 
safest position we can well imagine is that of being horizon- 
tally suspended in a hammock by silk cords in the middle 
of a room, and perhaps the next, that of lying on a mattress 
or feather bed on a wooden bedstead the materials of which 
are very imperfect conductors. It is scarcely necessary to 
say that if the bedstead be in the middle of the room, at a 
distance from the wall, the danger will be still less. 

It may perhaps be well to dwell for a moment on the ex- 
planation of the foregoing statement. Let us suppose a man 
to be standing on a large piece of bees-wax, which is almost 
a perfect non-conductor, and exposed to a cloud highly 
charged with positive electricity. A portion of the natural 
electricity of his head would be drawn down into his feet; 
the former would become negatively electrified and attract 
the lightning of the cloud, while the latter would repel it; 
the tendency to be struck would be on account of the dif- 
ference of these two actions. If the man stepped off the non- 
conducting wax on to the earth the redundant electricity 
which had collected in his feet would be discharged, his 
head would become still more negatively electrified, the re- 
pulsion which existed, in the other case would disappear, 
while the attraction would be increased, and hence the ten- 
dency to be struck would be much greater. 

Let us next consider what would take place if a man 
should be extended horizontally on a large disc of beeswax. 
In this case the upper part of the body, or that toward the 
sky, would become negative, and the lower part, or that in 
contact with the beeswax, would become positive, and the 
attractions and repulsions would be exhibited as in the first 
instance, but with less energy, because their foci would be 
much nearer each other, and consequently they would act 
with almost equal effect; while the repelled electricity not 
having space into which to descend, a less quantity of it 
would be repelled from each point of the upper surface. If 



374 WRITINGS OP JOSEPH HENRY. [1855- 

the disc of wax were placed above the man's head while in 
the standing position it would not screen the repulsive energy 
in the cloud, which like gravitation acts through all bodies; 
the induction would take place as before, the head would 
become highly negative, while the natural electricity which 
had been driven down would escape into the earth. The 
effect would therefore be the same as if the individual were 
standing on the earth without the intervention of the non- 
conducting material. A descending bolt would be attracted 
towards the head, and if the tenacity of the bees-wax were not 
sufficient to withstand a disruptive discharge, the body would 
be injured. From a mis-apprehension of these principles 
it has been supposed that the protection is increased by 
a slight covering over the body of silk or feathers, or by in- 
terposing a plate of glass between the sky and body; but 
it is well known that fowls and other large birds are struck, 
the slight covering of feathera affording no protection while 
the feet are in connection with the earth. 

From the conducting capacity of the soot usually lining 
a chimney, and of the smoke and heated air which ascend 
from the flue, it will be clear that the vicinity of the fire- 
place during a thunder-storm is not the safest position that 
may be chosen in a house. A person leaning out of an open 
window may also not be in a very safe position, because the 
outside of the house, wetted with rain, will be rendered a 
partial conductor, and a descending charge along the wall 
may reach the body projecting beyond the surface. The in- 
duction is always greater where there is a large amount of 
conducting material, hence barns filled with damp hay will 
be more liable to be struck than when empty. Besides the 
action of induction in this case, it is generally supposed that 
the danger is increased by the ascent of vapor from the 
barn at the season mentioned ; and this supposition, which 
is in accordance with scientific principles, is apparently 
borne out by observation. 

On the principle of the increase of induction in the col- 
lection of a large number of conducting bodies in a given 
space, the assemblage of persons in churches, or other places 



-1859] WRITINGS OF JOSEPH HENRY. 375 

of public meetings, increases the tendency of lightning to 
fall on the edifice. The inductive action will be slightly in- 
creased when the audience assumes a standing position. 
For a similar reason sheep which are crowded together dur- 
ing a storm are frequently killed by lightning. The fact 
has several times been noticed that when a discharge passes 
through a number of animals arranged in a straight line, 
those which are at the extremities of the row suffer most ; 
and this has been observed even when the animals were not 
in immediate contact with each other, as for example a 
number of horses in a series of stalls. It is probable that 
the heated air between the horses may have served as a con- 
ducting medium, and that the effect can be referred to the 
increase pf intensity which always takes place in the electri- 
cal discharge at the points where the air is ruptured, or 
where the electricity enters and passes out. 

The probability of injury from lightning is slight, even 
in this country where thunder-storms are comparatively 
frequent in the summer; and though it may be well to 
observe proper precautions, yet on account of the small risk 
to which we are subjected we should not deprive ourselves 
of the gratification of observing and studying one of the 
most sublime spectacles of nature; and indeed we know of 
no better way of overcoming the natural dread which many 
persons have of this meteorological phenomenon than by 
becoming interested in its scientific principles, and in study- 
ing, in connection with these, its appearance and effects. 

Effects of the introduction of gas and water pipes, — Since the 
use of gas has become so general in our cities as to be con- 
sidered almost one of the essentials of civilized life, a new 
source of danger has been introduced. Persons who repu- 
diate the use of lightning-rods because they attract the elec- 
tricity from the clouds should reject the introduction of gas 
— ^particularly in the upper stories of their dwellings, since the 
perpendicular pipes must act as the most efficient conductors 
between the cloud and the earth. "We say the most efficient 
because they are connected below the ground with a plexus 
of pipeSy in many cases of miles in extent, the whole of which 



tj. 



376 WRITINGS OP JOSEPH HENRY. [1855- 

is rendered highly negative by the induction of a largo cloud ; 
and since this action takes place with as much eflBciency 
through the roof of a house and the chamber floors as it does 
through the open air, a gas-pipe within a house, (in propor- 
tion to its height) would powerfully attract any discharge 
from a cloud in its vicinity. 

To obviate the danger from this source, the lightning-rod 
which rises above the top of the building should be placed 
in immediate metallic contact with the plexus of gas-pipes 
outside the house. If as is very frequently the case, the rod 
is made to terminate by simple insertion of a few feet in the 
dry earth, while the gas-pipe is connected with mile3 of metal- 
lic masses, rendered highly negative by induction, the path of 
least resistance, or of most intense induction from the cloud to 
tlie earth, will be down the rod to some point opposite the gas- 
pipe, then through the house and down the pipe into the 
great receiver below. This conclusion, from the theory, is 
fully borne out by observation. On Friday evening. May 
14, 1858, a house in Georgetown, D. C, was struck by light- 
ning, and on Saturday, the next evening, another house was 
struck in Washington, on Seventeenth street, north of Penn- 
sylvania avenue. The writer carefully examined the condi- 
tions and effects in both cases, and found them almost identi- 
cally the same. The houses were simihirly situated, with 
gable ends north and south, and attached to the west side of 
each was a smaller back building. The lightning-rod of the 
house at Georgetown was placed on the southern gable. It 
terminated above in a single point, and its lower part was in- 
serted into hard ground, through a brick pavement, to tlie 
. depth of about five feet. The lightning fell upon the point, 
(which it melted,) passed down the rod until it came to the 
level of the eaves, thence leaving the conductor, it passed hori- 
zontally along the wet clapboards to the southwest eave or cor- 
ner of the house, thence down a tinned iron spout to the tin 
gutterundertheroofoftheback building, and thence it pierced 
the wall of the house opposite the point on the outside of 
the back building corresponding to the position of a gas-pipe 
in the interior, after which no further effects of it could bo 



'J. 



-1959] WRITINGS OP JOSEPH HENRY. 377 

observed. A small portion of the charge however diverged 
to a second gas-pipe in an adjoining room. The back build- 
ing was of wood, and the passage of the charge appeared to 
be facilitated by a large nail. The discharge was marked 
throughout its course by the effects it produced: 1st, the 
point of the rod was melted ; 2d, a glass insulating cylinder 
through which the upper part of the rod passed was broken 
in pieces ; 3d, the horizontal clapboard extending from the 
rod Jto the eave was splintered ; 4th, the tin of the gutters and 
spout exhibited signs of fusion ; 5th, the plaster was broken 
around the hole through which the charge entered the house. 

The lightning-rod of the house which was struck in Wash- 
ington was placed on the north gable ; the electricity left 
the conductor at the apex of the roof, descended along the 
angle of the coping and the roof, which was Imed with tin, 
to the northwest eave of the main building, thence south- 
ward along a tin gutter until it met a perpendicular tin 
spout, which conducted it to a point on the outside of the 
back building corresponding to a gas-pipe within ; it then 
pierced a nine-inch brick wall and struck the gas-pipe, that 
which was embedded in the wall of the main building, at 
the distance of 15 inches horizontally north of the hole which 
it pierced in entering the interior. A lady was sitting with 
her back toward the point where the discharge entered the 
gas-pipe, at the distance of 18 inches, and though she was 
somewhat stunned at the time, and perceived a ringing 
sensation in her ears for some time after, she received no 
permanent injury. 

At the last meeting of the American Association, Pro- 
fessor Benjamin Silliman, Jr., described two instances of a 
similar character, in which the discharge from the cloud 
struck twice, in different years, the lightning-rod of the 
steeple of a church in New Haven, left the conductor and 
entered the building, to precipitate itself on the gas-pipes of 
the interior. The remarkable fact was stated in connection 
with this occurrence, that the joinings of the gas-mains 
under the street on the outside of the building were loosened, 
apparently by the mechanical efifect of the discharge, and 



378 WRITINGS OP JOSEPH HENRY. [1855- 

the company was obliged to take them up and repair the 
damage to prevent the loss of gas. An occurrence of this 
kind might perhaps lead the proprietors of gas-works to ob- 
ject to the proposition of connecting the end of the rod with 
their mains ; but they should recollect that if means be not 
furnished to prevent the danger consequent upon the use of 
gas, a less amount of the article will be consumed ; and fur- 
thermore that giving more eflSciency to the inductive action 
of the rod on the cloud by the connection we have pro- 
posed, the tendency to a discharge will be lessened; and 
finally, that if the connection be not formed, the discharge 
from the cloud will itself find the main through the gas- 
pipes within the house. 

There is another source of danger of a similar character 
in cities supplied with water from an aqueduct; the pipes in 
diflerent stories of the buildings, connected with the water 
mains which under-lie the city, in most intimate connection 
with the earth, are subject to a powerful induction from the 
cloud above, and therefore will attract any discharge which 
may be passing in their vicinity, or even determine the 
point at which the rupture of the stratum of air between the 
cloud and the house shall take place. In this case the light- 
ning-rod should also be connected with the pipes under 
ground, in order that the .induction through the rod should 
be as perfect as possible, and that the consequent attraction 
may confine the charge and transmit it entirely to the large 
mains, and from them to the earth. Houses are sometimes 
supplied with water from the roof, collected in tanks in the 
loft, whence it is distributed by pipes to diflerent parts of 
the building. This arrangement also tends to invite the 
lightning in proportion to the perpendicular elevation of 
this system of conductors. The lower ends of these are not 
usually in very intimate connection with the earth, and 
therefore a less powerful induction takes place than in the 
other instances we have mentioned. They should however 
be placed as in the preceding case in good metallic connec- 
tion with the lightning-rod on the outside of the house. 
The same remark applies to steam and hot-water pipes used 
for heating large buildings. 



380 WRITINGS OF JOSEPH UENBY. [185S- 

this prediction, on the occurrence of the fi^ thunder-storm 
the apparatus received a discharge from the cloud, which 
fused several holes in the upper part of the ball and indented 
the surface, but fortunately did no damage to the building. 
The apparatus was then removed, and the ball deposited in 
the museum of the Smithsonian Institution as an interest- 
ing ilhistration of the chemical and mechanical effects of a 
discharge of lightning. 

Effects of telegraph wires. — In 1846, the Hon. S. D. Ingham, 
of Pennsylvania, requested the opinion of the American 
Philosophical Society as to whether security in regard to 
accidents from lightning is increased or lessened by the 
erection of telegraph wires, the poles of which are placed 
by the side of the roads along which persons with horses 
and carriages are constantly passing. The subject was 
referred to the writer, from whose report in regard to it 
the following facts and deductions are given. * The wires 
of a telegraph are liable to be struck by a direct charge 
from the clouds, and several instances of this kind have been 
observed. About the 20th of May, 1846, the lightning struck 
the elevated part of the wire which is supported on a high 
mast where the wire crosses the Hackensack river. The 
fluid passed along the wire each way from the point which 
received the discharge for several miles, striking off at reg- 
ular intervals down the supporting poles. At each point 
whore the discharge took place along a pole a number of 
sharp explosions were heard in succession, resembling the 
rapid reports of several rifles. During another storm the 
wire was struck in two places on the route between New 
York and Philadelphia. At one of these places twelve poles 
were struck and at the other eight. In some instances the 
lightning has been seen coursing along the wire like a stream 
of light, and in one case it is described as exploding from 
the wire in several places, though there were no bodies in 
the vicinity to attract it from the conductor. 

That the wires of the telegraph should be frequently struck 

* [Proceedings Am. Phil. Society, June 19, 1846, see ante, vol. i, p. 244.] 



-1859] WRITINGS OF JOSEPH IIENUY. 381 

is not surprising when we consider the great length of the 
conductor, and consequently the many points through 
which it must pass along the surface of the earth peculiarly 
liable to receive the discharge from the heavens. Besides 
this, from the great length of the conductor, its natural elec- 
tricity, driven to the farther end or ends of the wire, will be 
removed to a great distance from the point immediately 
under the cloud, and hence this will be rendered more in- 
tensely negative and its attractive power thereby highly in- 
creased. It is not probable however that the attraction, what- 
ever may be its intensity, of so small a wire as that of the 
telegraph can of itself produce an electrical discharge from 
the heavens, although if the discharge were started from 
some other cause, (such as the attraction of a large mass of 
conducting matter in the vicinity,) the attraction of the wire 
might be sufficient to change the direction of the descending 
bolt and draw it, in whole or in part, to itself. It should 
be recollected also that on account of the perfect conductivity 
of the wire, a discharge on any one point of it must affect 
every other part of the connected line although the whole 
may be several hundred miles in length. 

That the wire should give off a discharge to a number of 
poles in succession is a fact that might have been anticipated, 
since the electricity would by its self-repulsion tend to send 
a portion of itself down the partial conducting pole, while 
the remaining part, attracted by the wire in advance of itself, 
rendered negative by induction, would continue its passage 
along the metal until it met another pole, when a new di- 
vision of the charge would take place, and so on. The several 
explosions in succession, heard at the same pole, are explained 
by the fact that the discharge from the cloud does not gen- 
erallj^ consist of a single wave of electricity, but of a number 
of discharges in the same path in rapid succession, so as in 
some cases to present the appearance of a continuous dis- 
charge of a very appreciable duration; and hence the wire 
of a telegraph is capable of transmitting an immense quan- 
tity of the fluid thus distributed in time, over a great length 
of the conductor. 



382 WRITINGS. OP JOSEPH HENRY. [1855- 

From the foregoing in regard to the direct discharge, we 
think the danger to be apprehended from the electricity 
leaving the wire and striking a person on the road is small. 
Electricity of suflScient intensity to strike a person at the dis- 
tance of twenty feet from a perfectly insulated wire would 
in preference be conducted down the nearest pole. It will 
however in all cases be most prudent to keep at a proper 
distance from the wire during the existence of a thunder 
storm, or even at any time when the sound of thunder is 
heard in the distance. 

In case of wires passing through cities and attached to 
houses they should be provided at numerous points with 
electrical conductors to carry oflF the discharge to the earth. 
These consist of copper wires intimately connected with the 
earth by means of a plate of metal at the lower end, extend- 
ing up the pole or side of the house, and terminating in a 
flat plate above, parallel to another plate of metal depending 
from the wire of the telegraph. The two plates are separated 
by a thin stratum of air, or some other non-conducting ma- 
terial, through which the intense discharge from the clouds 
will readily pass and be conducted to the earth, while the 
insulation of the wire for the purposes of the telegraph is 
un-impaired. 

There are other electrical phenomena connected with the 
telegraph which, though frequently annoying to the operator, 
are not attended with the same degree of danger to his per- 
son. These are immediately referable to induction at a 
distance, and consist entirely in the disturbance of the natu- 
ral electricity of the wire. Suppose a thunder cloud to be 
driven by the wind in such a direction as to cross at right 
angles, for example, the middle of a long line of telegraph 
wire. During the whole time the cloud is approaching the 
point of its path directly above the wire, the repulsion of the 
redundant electricity of the former will constantly drive the 
natural electricity of the latter farther and farther along the 
line, so that during the approach of the cloud a continuous 
current will exist in each half of the line. When the centre 
of action of the cloud arrives at the nearest point of. the wire 



384 , WRITINGS OP JOSEPH HBNRi. 

During very warm weather a feeble current is observed at 
diflferent periods of the day, which may be referred to thermo- 
electricity. It is well known that when one end of a long 
conductor is heated and the other cooled, a current of elec- 
tricity will pass from the hotter to the colder extremity, and 
this will be continued as long as the difference of tempera- 
ture exists. Extended lines in a north and south direction 
are most favorably situated for observing a current of this 
class. Currents of electricity of sufficient intensity to set 
fire to pieces of paper, have also been observed in connection 
with the appearance of the aurora borealis 

Means of Protecting BuUdinga. 

Although much has been written and said in disparage- 
ment of tire admirable invention of our illustrious country- 
man, Franklin, yet an attentive consideration of all the 
facts, even independent of theory, fully establishes its great 
importance. 

1st. It is well known, from general experience, that light- 
ning directs itself to the most elevated portions of edifices. 
Cotton Mather declares that lightning is under the immedi- 
ate direction of the " Prince of the powers of the air," because 
church steeples are more frequently struck than any other 
objects. It is therefore evident that the preservative means, 
whatever they may be, should be applied to the upper por- 
tions of a building. 

2d. If other conditions be the same, lightning directs itself 
in preference — to metals. When therefore a mass of metal 
occupies the more elevated portion of a house we may be 
nearly certain that lightning, if it falls upon the building, 
will strike that point. 

3d. Lightning when it enters a metallic mass does mis- 
chief only where it quits the metal, and in the vicinity of 
the point at which it issues. A house therefore entirely 
covered with metal would be safe, provided this covering 
were intimately connected with the ground by metallic con- 
ductors of sufficient size. When there are upon the roof 
or in any of the upper stories of an edifice several dis- 



-1859] WRITINGS OF JOSEPH HENRY. 385 

tinct metallic masses completely separated from each other, 
it will be difficult to tell which of them will be struck in 
preference. The safest practice is to unite all these masses 
by rods or bands of iron, copper, or other metal, so that each 
of them may be in metallic communication with a rod 
which may transmit the lightning to the damp earth. 

" We thus deduce from facts established by observation 
alone without borrowing anything from theory," says Arago, 
"a simple, uniform, and rational means of protecting build- 
ings from the eCTects of lightning. But when we refer, in 
addition to these facts, to the precise principles or laws of 
electrical action, as deduced from cautious and refined ex- 
periments in the laboratory, we are enabled to give rules for 
the protection of buildings which, when properly observed 
reduce almost to insignificance the danger to be apprehended 
from the ordinary occurrences connected with the terrific 
exhibitions of thunder-storms." 

From what has been said on the principles of induction, 
and also on the fact of the negative condition of the earth, it 
will be readily perceived that the upper end of an elevated 
conductor must become highly negative under the repulsive 
energy of a positive cloud, and though it may not be suffi- 
cient in itself to cause a rupture of the thick stratum of air 
intervening between the cloud and the earth, yet if a dis- 
charge does take place in the vicinity of this body, it will 
be drawn toward it, and if the conductor extends to the 
earth, and is in intimate connection with the damp ground, 
the discharge will pass innoxiously into this great reservoir. 
We further know from theory as well as experiment and ob- 
servation, that the intensity of attraction is increased when 
the conductor is terminated above in a single sharp point. 
Although the attraction at a distance may be greater on a 
metallic globe of a few feet in diameter than on a metallic 
point, (since the former is able to receive a greater induced 
charge, which by the well-known law of attraction will act 
as if the whole were concentrated at the centre of the sphere,) 
yet the intensity of action of the point and its tendency to 
open a passage through the air is so great that it is preferred 
in protecting a given circumscribed space from lightning. 

25-2 



386 WRITINGS OF JOSEPH HENRY. [1855- 

The question has been agitated whether one point or a 
number on the same stem is to be preferred? But this 
question may be readily settled, provided the reason for pre- 
ferring a point to a ball or a globe is legitimate, since the 
surface of a ball itself may be considered as made up of an 
infinite number of points, and therefore a number of points 
close together must re-act upon each other, and thus ap- 
proximate in result the effect of a continuous spherical sur- 
face. In the case of three points on the same stem, the 
whole amount of inductive eflTect produced in the rod is 
practically divided into three parts, and is therefore less con- 
centrated than in the case of one point; and although at a 
distance the effect of the three may be equally energetic, yet 
the one point tends more effectually to rupture the air, and 
open (so to speak) a passage for the discharge from the cloud. 

In reference to the subject of the termination of rods by 
balls or points, much discussion took place 6n the early in- 
troduction of the invention of Franklin, and the subject was 
elucidated by a very ingenious experiment made by Beccaria, 
in 1763, which is quoted by Arago. On the roof of a church at 
Turin this eminent electrician erected a rod of iron insulated 
on one of the flying buttresses. The upper part of this rod, 
which was terminated by a single metallic point, was hinged 
a few inches below the top, so that by merely pulling a string 
the point could be directed horizontally, upward, or down- 
ward. When the point was pulled downward during the 
presence of a thunder-cloud in the zenith, the lower end of the 
rod gave no sparks; but when the point was suddenly directed 
upward, in a few moments sparks appeared. When the point 
was downward, the rod presented a blunt termination toward 
the sky ; when upward a sharp point. It might be well to 
repeat this experiment with some slight variation in the ap- 
paratus, in order to establish or dis-prove, by direct observa- 
tion, the inference from theory that a single point acts more 
energetically than three or four points, terminating the same 
rod. The substance which terminates the conductor should 
be such as to preserve its form when subjected to the action 
of the weather, and be infusible by a stroke of lightning. 



388 WRITINGS OF JOSEPH HEXRY. [1855- 

metal formed part of the building or the roof. Observations 
have been recorded of parts of houses being struck within 
the limit just mentioned as that of protection ; but scarcely 
any of them are satisfactory in determining the point, since 
it appears from the evidence that in several cases there 
were separate masses of metal which formed independent 
conductors, and in the other coses there was no evidence 
that the rod was in proper connection with the earth. In 
order to protect an extensive building, it will evidently be 
necesar}' to arm it with several lightning-conductors, and 
the less their height, the greater must be their number. 

In the case of a tall steeple, it may be well to establish 
jx>ints at different elevations, by branches from the main 
rod ; for if it be true that the rod merely attracts the light- 
ning which has been determined by the earth itself, or some 
material under the ground, the discharge in its passage along 
the line of least resistance to the point at which it was aimed, 
may not be made to deviate from its direct course by the at- 
traction of the distant elevated point, and may strike a lower 
portion of the building. Suppose for example a thunder- 
cloud is on the west side of a high steeple, and the point of 
attraction, which may be damp earth, a pool of water, or 
other conducting material on the surface or under the ground 
at the east end of the church : the discharge from the cloud, 
in its passage to the point of attraction, may strike a lower 
portion of the building, the action of the elevated point not 
being sufficient to deflect it from its course. This inference 
is in accordance with actual observation. Mr. Alexander 
Small wrote to Franklin, from London, in 1764, that he had 
seen in front of his window a very vivid and slender light- 
ning discharge pass low down, without a zig-zag appear- 
ance, and strike a steeple below its summit. 

It becomes a matter of interest to ascertain whether the 
action of an assemblage of conductors, such as is usually 
found in cities, produces any sensible effect in diminishing 
the electrical intensity of the cloud, or in other words whether 
their united influence produces any sensible diminution of 
the destructive effects of thunder-storms. Late researches 



-1839] WRITINGS OF JOSEPH HENRY. 389 

have shown that but a comparatively small amount of de- 
velopment of electricity is sufficient to produce great mechan- 
ical effects. Faraday has even asserted that the quantity of 
electricity necessary to de-composo a single grain of water, 
(and consequentl}^ the electricity which would be evolved by 
the re-composition of the same elements) would bo sufficient 
to charge a thunder cloud, provided the fluid existed in the 
free state in which it is found at the surface of charged con- 
ductors. A similar inference may be drawn from the great 
amount of electricity developed by the friction of the small 
quantity of water existing in steam, as the latter issues 
through an orifice connected with the side of the boiler. We 
also find that an. iron rod of three-fourths of an inch in 
diameter, is of sufficient size to transmit to the earth with- 
out any danger to surrounding objects a discharge from the 
clouds, which may bo attended with a deafening explosion 
and with a jar of thunder powerful enough to shake the 
building to its foundation. 

The intrepid physicist, DeRaumer, sent a kite up into 
the air to the height of 400 or 500 feet, in the cord of which 
was inserted a fine wire of metal. During a thunder-storm 
he drew from the lower extremity of the cord not mere sparks 
but discharges nine or ten feet long and an inch broad. 

Beccaria erected a lightning-rod which was separated in 
the middle by an opening, the upper part being entirolj'^ 
insulated. During thunder-storms intense discharges darted 
incessantly through the opening. So constant were these 
that neither the eye nor the ear could readily perceive the 
intermission. 

"No physicist," says Arago, "will contradict me when I say 
that each spark taken singly would have given a shock 
attended with pain, that ten sparks would have numbed a 
man's arm, and a hundred would have proved fatal. Now 
a hundred sparks passed in less than ten seconds, and hence 
in every ten seconds there was drawn from the cloud a 
quantity of electrical energy sufficient to kill a man, and six 
times as much in every minute." Arago calculates in this 
way that all the lightning conductors of the building in 



390 WRITINGS OP JOSEPH HENRY. [1855- 

which the experiment was tried took from the clouds as much 
lightning as would have been sufficient in the short space of 
an hour to kill upwards of three thousand men. From the 
foregoing facts and conclusions wo may infer that the light- 
ning-rods of a city have considerable effect in silently dis- 
charging the clouds, and in preventing explosions which 
would otherwise take place; but we must recollect that on 
account of the upward rushing of the moist air, the elec- 
tricity of the cloud is constantly renewed. 

We cannot suppose that the sparks observed by Beccaria 
in his experiment, and the ringing of bells by Franklin, were 
due entirely to the electricity immediately received from the 
cloud. By the powerful induction of the redundant elec- 
tricity of the latter, and the negative action of the earth be- 
neath, the natural electricity of the top of the rod would be 
forced down into the earth, the point would become intensely 
negative, and in this condition would draw from the air 
around streams of electricity, and in this way a large volume 
of air around the top of the rod would become negatively 
electrified ; and in case a discharge of lightning took place 
its first effect would be to neutralize or fill up, as it were, 
this void of electricity in the large mass of air surround- 
ing and above the top of the rod, before the remainder of the 
discharge could pass to the earth. The peculiar sound which 
is heard when a discharge from a thunder-cloud is transmit- 
ted through a lightning-rod may possibly be attributed to 
this cause. 

The Smithsonian building, with its high towers, situated 
in the middle of a plain, at a disUxncc from all other edifices, 
is particularly exposed to discharges of lightning, and we 
have reason to believe that in as many as four instances 
within the last ten years the lightning has fallen upon the 
rods and been transmitted innoxiously to the ground. 

In two of the instances the lightning was seen to strike 
the rod on one of the towers; in a third, a bright spark due 
to induction and attended with an explosion as loud as that 
of a pistol was perceived ; and in the fourth instance, although 
the platinum top of the rod, which was one hundred and fifty 



•1859] WRITINGS OP JOSEPH HENRY. 391 

feet from the surface of the ground, was melted, the dis- 
charge was transmitted to the earth without any other effect 
than a slight inductive shock given to a number of persons 
standing at the foot of the tower. In three of these cases the 
peculiar sound we have mentioned was observed; — first, a 
slight hissing noise, and afterward the loud explosion, as if 
the former were produced by the effect of the discharge on 
the air in the immediate vicinity of the rod, and the loud 
noise from that on the air at a. more distant point of its path. 
The writer was led to reflect upon this effect of the rod by 
a remarkable exhibition he witnessed during a thunder- 
storm at night in 1856. He was in his office, which is in 
the second story of the main tower of the Smithsonian edifice, 
when a noise above, as if one of the windows of the tower 
had been blown in, attracted his attention: an assistant who 
was. present was requested to take his lantern and ascertain 
what had happened. After an absence for some time he re- 
turned, saying he could discover nothing to account for the 
noise, but that he had heard a remarkable hissing sound. 
The writer then ascended to the top of the tower, and stood 
in the open trap-door with his head projecting above the 
flat roof within about twelve feet of the point of the light- 
ning-rod. No rain was falling, though an intensely black 
cloud was immediately overhead and apparently at a small 
elevation; from different parts of this, lightning was con- 
tinually flashing, indeed the air around the top of the tower 
itself appeared to be luminous. But the most remarkable 
appearance was a stream of light three or four feet long issu- 
ing with a loud hissing noise from the top of the lightning- 
rod. It varied in intensity with each flash, and was almost 
continuous during the observation. Although the whole 
appearance was highly interesting, and produced a consider- 
able degree of excitement, yet the writer did not deem it 
prudent to expose himself to the direct or even inductive 
effect of a discharge under such conditions, thinking as ho 
did with Arago, that however our vanity might prompt us 
to boast of the acquaintance of some great lords of creation, 
it is not always desirable to seek their presence or court 



392 WRITINGS OP JOSEPH HENRY. [1855- 

much familiarity with them. The effect of the rod in this 
case on the surrounding air and on the cloud itself by invis- 
ible induction must have been quite remarkable. 

Action of lig1dnxn{j'rod%. — The question as to whether the 
lightning-rod actually attracts the electricity from a distance 
has been frequently discussed. "It will be found," says Sir 
W. Snow Harris, " that the action of a pointed conductor is 
purely passive. It is rather the patient than the agent ; and 
such conductors can no more be said to attract or invite a 
discharge of lightning than a water-course can be said to 
attract the water which flows through it at the time of heavy 
rain." This statement does not, as it appears to us, present 
a proper view of the case. From the established principles 
of induction, it must be evident that all things being equal 
a pointed rod, though elevated but a few feet above the 
ground, would be struck in preference to any point on the 
surface, and the propositions as to the space which can be 
protecteil from a discharge of lightning are founded on the 
supposition that the direction of the discharge can be changed 
by the action of the rod at a distance and the bolt drawn to 
itself. The true state of the case appears to us to be as fol- 
lows: 

1st. An elevated pointed rod, erected for example on a 
high steeple, by its powerful induction diminishes the in- 
tensity of the lower part of the cloud, and therefore may 
lessen the number of explosive discharges to the earth. 

2d. If an explosive discharge tjxkes place from the cloud 
due to any cause whatever, it will bo attracted from a giver 
distance around to the rod, and transmitted innoxiously to 
the earth. 

A too exclusive attention to either one or the other of these 
actions lu\s led to imperfect views as regards the office of 
the li2rhtnin*::-nxl. On the one hand, some have considered 
that the whole olloct of the roil is to lessen the number of 
disoluu*ges in the way described, and have considered 
it im{K>ssiMe that an explosive discharge could take place 
on a pointeil conductor. But this is not the case, as was 
shown by Mr. Wilson many years ago by his experiments 



-1859] WRITINGS OP JOSEPH HENRY. 393 

in London. It is true, that when a needle is presented to a 
charged conductor, the electricity is drawn off silently with- 
out an explosion, and this is always the case if sufficient time 
be allowed for the electricity to escape in this way. But if 
the point be suddenly brought within striking distance of 
the conductor by a rapid motion, such as would be produced 
by the movement of a horizontal arm carrying the jioint im- 
mediately under the conductor in an instant, an explosive 
discharge will take place. In this case sufficient time is not 
given for the slower transmission of the electricity by what 
has been denominated the glowing discharge, and a rupture 
of the air is produced as in the action of a conductor termi- 
nated by a ball. 

It would follow from this that in the case of a rapidly-mov- 
ing cloud across the zenith of a rod, there would be a greater 
tendency to an explosive discharge on the point than when 
the cloud was nearly stationary. For a similar reason, if a 
point connected with the earth by a wire be directed toward 
an insulated conductor, and the latter be suddenly electrified 
by a discharge from a second conductor, an explosion will 
take place between the first conductor and the point. A 
similar effect would be produced if a lower cloud received 
a sudden discharge from one above it, a case which prob- 
ably frequently occurs in nature. Mr. Wise informs us that 
when a discharge takes place from the base of a cloud to the 
earth, a discharge is seen to pass between the upper and 
lower part of the cloud. (A condition shown in Fig. 19.) We 
are warranted from the foregoing facts, as well as from the 
numerous examples in which lightning has actually been 
seen to fall upon pointed rods explosively, and the number 
of points which have been melted, to conclude that the rod 
under certain conditions does actually attract the lightning, 
though when properly constructed it transmits it without 
disturbance to the earth. 

It has been denied by some that the point has any per- 
ceptible influence in lessening the number of strokes from 
a cloud, but this proposition can scarcely be doubted when 
i¥e reflect upon the fact that it is not necessary to entirely 



394 WRITINGS OF JOSEPH HENRY. [IdSS- 

discharge a cloud in order to prevent a rupture of the air, it 
being only necessary to draw off a quantity of the fluid suf- 
ficient to reduce it just below that which is required to pro- 
duce the explosion ; and for this effect there may be required 
but a very slight diminution in the intensity of a cloud 
which is at about the striking distance, to prevent an explo- 
sion, particularly when we consider the prodigious number 
of sparks which during thunder-storms were silently with- 
drawn from the cloud by the pointed rod erected by Beccaria. 

Arago has collected a large number of instances, from 
which it appears that the erection of a rod lessened the num- 
ber of the explosive discharges. 

The Cam|>anile of St. Marks, at Venice, from the multi- 
tude of the pieces of iron in its construction, was in a high 
decree exjwsed to danger from lightning, and in fact prior 
to 1776, had been known to be stnick nine times. In 
the b^inning of that year a conductor was placed upon it, 
and since that time the edifice has been un-injured by light- 
ning. 

Pn>vious to 1777, the tower of Sienna was frequently 
struck, and on every occasion much injured. In that year 
it was provided with a conductor, and has since received 
one discharge, but with no damage. 

In the case of a church at Carinthia, on an average four 
or live strokes of lightning annually were discharged upon 
the steeple until a conductor was erected, after which one 
stri^ke was received in five years. At the Valentino palace 
tho liixhtning conductors established by Beccaria, caused the 
oniiro disiip^x^anince of strokes of lightning which were pre- 
viously of frequent occurrence. 

The monument in London, although only accidentally pro- 
vidixl with a virtual conductor, appears to have been exempt 
fnnu damaire bv liditning for nearly one hundred and eighty 

years. 

The action of the rod in diminishing the intensity of the 
cloud however, can only be of a very temporary character, 
auvl cannot, as some have supposed, affect its subsequent 
state, or distirm it of its fulminating power, since its elec- 



-1859] WRITINGS OP JOSEPH HENRY. 395 

tricity is constantly renewed; a fact sufficiently demon- 
strated by the observation that a thunder storm, through its 
whole course of several hundred miles in extent, continually 
gives discharges to the earth. Notwithstanding the instances 
given by Arago of the diminution of discharges of lightning 
after the erection of the rod, the fact is established bj^ obser- 
vation, experiment, and theory, that the rod does attract the 
lightning, and that it receives the discharge not alone 
silentlj^ but explosively. The points of the conductors are 
frequently melted, and although in cases in which this 
occurs, the discharge passes harmlessly to the earth, yet in 
some instances the explosion might not have taken place 
had the rod not been present. 

The following instructive illustration of the action of a 
very elevated conductor in transmitting a discharge from a 
thunder cloud is furnished us by Mr. Henry J. Rogers, tele- 
graph engineer, who was himself an eye-witness of what he 
relates : 

" In accordance with my promise I will endeavor to give 
you a brief description of the effect produced by atmospheric 
electricity at the House Telegraph mast, erected at the Pali- 
sades on the west side of the Hudson river, in the vicinity 
of Fort Lee, New Jersey, and distant about ten miles from 
the City Hall, New York, during a terrific thunder storm 
which occurred on Friday, June 17, 1853, between three and 
four o'clock p. M., while I was on an official visit. 

" Before I proceed with the description it will be necessary 
to explain that the wires of the House and Morse telegraph 
lines cross the Hudson river between Fort Washington and 
the Palisades, inasmuch as this is the narrowest part of the 
river in the vicinity of New York, and the elevation of the 
land at the Palisades renders it a desirable place for suspend- 
ing the wires from one shore to the other, so as to allow 
vessels of large size to pass under them free from interruption. 

" The mast to support the wire was 266 feet in length, 
and was erected on the top of the columnar wall of the Pali- 
sades, which at this place is 298 feet above the river, as de- 
termined by trigonometrical measurement. The top of the 
mast was therefore 564 feet above the water, and was suf- 
ficiently elevated to allow for the unavoidable sagging of 
the telegraph wire, and to leave sufficient distance for vessels 
to pass beneath. 



396 WRITINGS OF JOSEPH HENRY. [1855- 

" It was composed of three pieces of heavy timber placed 
one above the other and fastened together by iron bands, to 
which were attached long iron braces or guys secured at the 
lower ends to the rock for the purpose of sustaining the mast 
in its perpendicular position. The braces or guys were 
formed of iron rods three-fourths of an inch in diameter, and 
painted black. The longer or outer ones, (those which were 
attached to the top of the mast and along which the electricity 
descended to the earth,) terminated about 32 paces from the 
lower end of the mast: they were composed of pieces of iron 
rod of thirteen feet in length, and each piece terminated in 
a bolt and shackle, thereby forming a series of links 30 in 
number. 

"A lightning-rod six feet long, three-quarters of an inch 
diameter, painted white, sharpened to a point, but not tip- 
ped with platinum, and secured at its lower end to the iron 
band to which were attached the upper set of guys, projected 
about two or three feet above the truck of the mast. The 
point of the rod was at the time in the center of a cedar bush 
in full foliage which had been placed there by the riggers 
when they completed the mast. 

"At 3 p. M., when the storm commenced, I placed myself 
in the railwa}' house at Fort Washington, a point distant 
about three-quarters of a mile from the mast at Fort Lee, on 
the opposite side of the river. From my position I could 
distinctly observe the gust as it advanced from the south- 
west; and from the heat of the weather and appearance of 
the clouds I expected to witness heavy discharges of atmos- 
pheric electricity, and prepared my mind to observe the 
effects of the storm on the mast at Fort Lee, having frequently 
expressed a desire to witness a thunder-storm in the vicinity 
of the mast, as I felt assured the iron rod and guys would 
protect it from injury. 

"As the gale increased the clouds advanced with a heavy 
atmosphere, and accompanied with frequent discharges of 
lightning and loud thunder. When it approached the mast 
the foremost cloud assumed the shape of an inverted cone, 
(similar to those I have witnessed in the Gulf of Mexico, 
forming a water-spout;) and I soon observed a terrific flash 
of lightning descend by the southern iron guy clearly 
defining its form and every link of the guy as though it 
were a rod of red-hot iron; and this appearance continued 
for at least four seconds, followed by three or four heavy 
peals of thunder in rapid succession, during which time 
the lightning appeared to flow in a continued stream of 



898 WRITINGS OP JOSEPH HBNUY. [1895- 

instructive. The descent of the visible vapor in the form of 
an inverted cone is a plienomenon which will be considered 
of special interest, particularly by those who ascribe the 
motive power of a tornado entirely to electricity. 

The continuance of the discharge during four seconds is 
in accordance with other instances which have been fre- 
quently observed, and is to bd attributed to a series of dis- 
charges in rapid succession through the same path. 

Tlie appearance of light along the whole course of the rods 
forming the guy may be attributed to the circumstance that 
the metal at the time of the discharge was covered with a 
thin stratum of water into which tlie electricity was pro- 
jected by its self-repulsion, and on account of the imperfect 
conductibility of the liquid, gave rise to the phenomena ob- 
served. 

This may be illustrated experimentally by discharging 
an electrical battery through a slip of tin foil wetted with a 
thin stratum of water. The discharge which would be in- 
sensible along the dry metal becomes luminous through its 
whole course. 

While this account of Mr. Rogers clearly shows the at- 
tractive {K>wer of an elevated conductor under particular 
circumstances, it also proves the fact that an edifice may be 
pR>tocteil from harm, provided it be furnished with a suffi- 
cient number of proi)erly constructed rods. 

Construction of lightning-rods. — Electricity (as we have seen 
— page 342,) tends to pass at tlie surface of a conductor of a 
sufficient size, but it does not follow from this tliat every in- 
crease of surface, the quantity of metal being the same, will 
tend to diminish the resistance of the conductor to tlie pass- 
ago of a discharge. From an imperfect view of the subject, 
many jx^rsons have supix>seil that merely flattening the light- 
ning-rod, and thus increasing the surface would tend to in- 
orvwso the cH)nducting j>ower, but it must be evident from 
the principle of repulsion, that in diminishing the distance 
botweon the two Hat surfaces, wc tend to increase the repul- 
sii>n botwivn the atoms, whic!i would pass parallel to the 
axis along the midiUe of each flat side, and thus, though the 



400 WRITINGS OF JOSEPH HENRY. [1855- 

borhood. Besides this, the irregularity in the motion of the 
electricity which is thus produced, must on mechanical prin- 
ciples interfere with its free transmission. Points should 
therefore be omitted along the course of the rod, since they 
can do no possible good, and may produce injury. 

We may conclude what we have said in regard to light- 
ning-rods by the following summary of directions for con- 
structing and erecting them : 

1st. The rod should consist of round iron, of not less than 
three-fourths of an inch in diameter. A larger size is pre- 
ferable to a smaller one. Iron is preferred, because it can 
be readily procured, is cheap, a sufficiently good conductor, 
and when of the size mentioned cannot bo melted by a dis- 
charge from the clouds. 

2d. It should be, through its whole length, in perfect me- 
tallic continuity; as many pieces should be joined together 
by welding, as practicable, and when other joinings are un- 
avoidable, they should be made by screwing the parts firmly 
together by a coupling ferule, care being taken to make the 
upper connection of the latter with the rod water-tight by 
cement, solder, or paint. 

3d. To secure it from rust the rod should be covered with 
a coating of black paint. 

4th. It should be terminated above with a single point, 
the cone of which should not be too acute, and to preserve 
it from the weather as well as to prevent melting it should 
be encased \vith platinum, formed by soldering a plate of 
this metal, not less than the twentieth of an inch in thick- 
ness, into the form of a hollow cone. Usually the cone of 
platinum, for convenience, is first attached to a brass socket 
which is secured on the top of the rod, and to this plan there 
is no objection. The platinum casing is frequently made 
so thin and the cone so slender, in order to save metal, that 
the point is melted by a powerful discharge. 

5th. The shorter and more direct the rod is in its course 

to the earth the better. Acute angles made by bending in 

the rod and projecting points from it along its course should 

be avoided. 

• 6th. It should be fastened to the house by iron eyes, and 



402 WRITINGS OF JOSEPH HENRY. [1855-^] 

should be united in good metallic connection with the light- 
ning-rods ; and in this case the perpendicular pipes convey- 
ing the water from the gutters at the eaves may be made to 
act the part of rods by soldering strips of copper to the metal 
roof and pipes above, and connecting them with the earth 
by plates of metal united by similar strips of copper to their 
lower ends, or better with the gas or water pipes of the city. 
In this case however the chimneys would be unprotected, 
and copper lightning-rods soldered to the roof and rising a 
few feet above the chimneys would suffice to receive the dis- 
charge. We say soldered to the roof, because if the contact 
were not very perfect, a greater intensity of action would take 
place at this point, and the metal might be burnt through 
by the discharge, particularly if it were thin. 

11th. As a general rule large masses of metal within the 
building, particularly those which have a perpendicular ele- 
vation, ought to be connected with the rod. The main por- 
tion of the great building erected for the world's exhibition at 
Paris is entirely surrounded by a rod of iron from which 
rises at intervals a series of lightning conductors, the whole 
system being connected with the earth by means of four wells, 
one at each corner of the edifice. 

The foregoing rules may serve as general guides for the 
erection of lightning-rods on ordinary buildings, but for the 
protection of a large complex structure, consisting of several 
parts, a special survey should be made, and the best form of 
protection devised whicli the peculiar circumstances of the 
case will admit. 

Numerous patents have been obtained in this country for 
improved lightning conductors, but as a general rule such 
improvements are of little importance. 

Such assumed improvements on the form of the lightning- 
rod recommended by the French Academy in 1823 would 
pre-suppose some important discoveries in electricity having 
a bearing on the subject; but after the lapse of thirty years 
the same Academy being called upon to consider the pro- 
tection of the new additions to the Louvre finds nothing 
material to change in the principles of the instructions at 
first given. 



404 WRITINGS OF JOSEPH HENRY. [1856 

been applied in the construction of the Smithsonian lecture- 
room. To apply them generally however in the con- 
struction of public halls, required a series of preliminary 
experiments. 

In a small apartment it is an easy matter to be heard 
distinctly at every point; but in a largo room, unless pro- 
vision be made in the original plan of the building for 
a suitable arrangement, on acoustic principles, it will be 
difficult, and indeed in most cases impossible, to produce the 
desired eflfect. The same remark may be applied to the 
lighting, heating, and ventilation, and to all the special 
purposes to which a particular building is to be applied. I 
venture therefore to make some preliminary remarks on the 
architecture of buildings, bearing upon this point, which, 
though they may not meet with universal acceptance, will 
I trust commend themselves to the common sense of the 
public in general. 

Ardiikdural limitations. — In the erection of a building, 
the uses to which it is to be applied should be clearly 
understood, and provision definitely made, in the original 
design, for every desired object. 

Modern architecture is not, like painting or sculpture, 
a fine art, par excellence. The object of these latter is to 
produce a moral emotion, — to awaken the feelings of the 
sublime and the beautiful; and we greatly err when we 
apj)ly their productions to a merely utilitarian purpose. To 
make a fire-screen of Rubens* Madonna, or a candelabrum 
of the Apollo Belvidere, would be to debase those exquisite 
productions of genius, and do violence to the feelings of the 
cultivated lover of art. Modern buildings are made for 
other purposes than artistic effect, and in them the aesthcti- 
oal must be subordinate to the useful; though the two may 
co-exist, and an intellectual pleasure be derived from a 
sense of adaptation and fitness, combined with a perception 
of harmony of parts, and the beauty of detail. 

The buildings of a country and an age should be ethno- 
logical expressions of the wants, habits, arts, and feelings of 
the time in which they wore erected. Those of Egypt, 



406 WRITINGS OP JOSEPH HENRV. [1856 

of iron and of glass requires an entirely different style 
from that which sprung from the rocks of Egypt, the masses 
of marble with which the lintels of the Grecian temples 
were formed, or the introduction of brick by the Romans. 

The great tenacity of iron, and its power of resistance to 
crushing, should suggest for it, as a building material, a far 
more slender and apparently lighter arrangement of parts. 
An entire building of iron, fashioned in imitation of stone, 
might be erected at small exercise of invention on the part 
of the architect, but would do little credit to his truthful- 
ness or originality. The same may be said of our modern 
pasteboard edifices, in which, with their battlements, towers, 
pinnacles, "fretted roofs and long drawn aisles," cheap and 
transient magnificence is produced by painted wood or 
decorated plaster. 

Ledare-room Acoustics, — ^To return to the subject of acous- 
tics, as applied to apartments intended for public speaking : 
While sound, in connection with its analogies to light, 
and in its abstract principles, has been investigated within 
the last fifty years with a rich harvest of results, few 
attempts have been successfully made to apply these princi- 
ples to practical purposes. Though we may have a clear 
conception of the simple operation of a law of nature, yet 
when the conditions are varied, and the actions multiplied, 
the results frequently transcend our powers of logic, and 
we are obliged to appeal to experiment and observation to 
assist in deducing new consequences, as well as to verify 
those which have been arrived at by mathematical deduc- 
tion. Furthermore, though we may know the manner in 
which a cause acts to produce a given effect, yet in all cases 
wc are obliged to resort to actual experiment to ascertain 
the measure of effect under given conditions. 

The science of acoustics as applied to buildings, perhaps 
more than any other, requires this union of scientific prin- 
ciples with experimental deductions. While on the one 
hand, the application of simple deductions from the estab- 
lished principles of acoustics would be unsafe from a want 
of knowledge of the constant3 which enter into our formula), 



1856] WRITINGS OP JOSEPH HENRY. 407 

on the other hand empirical data alona are in this case 
entirely at fault, and of this any person may be convinced 
who will examine the several works written on acoustics by 
those who are deemed practical men. 

Sound is a motion oif matter capable of affecting the ear 
with a sensation peculiar to that organ. It is not in all 
cases a motion simply of the air, for there are many sounds 
in which the air is not concerned ; for example, the impulses 
which are conveyed along a rod of wood from a tuning- 
fork to the teeth. When a sound is produced by a single 
impulse, or an approximation to a single impulse, it is 
called a noise; when by a series of impulses, a continued 
sound, &c.; if the impulses are equal in duration among 
themselves, a musical sound. This has been illustrated by 
a quill striking against the teeth of a wheel in motion. A 
single impulse from one tooth is a noise, from a series of 
teeth in succession a continued sound; and if all the teeth 
are at equal distances, and the velocity of the whesl is uni- 
form, then a musical note is the result. Each of these sounds 
is produced by the human voice, though they apparently 
run into each other. In speaking however a series of 
irregular sounds of short duration is usually emitted, — each 
syllable of a word constitutes a separate sound of appreciable 
duration, and each compound word and sentence an assem- 
blage of such sounds. It is no little surprising that in listen- 
ing to a discourse, the ear can receive so many impressions 
in the space of a second, and that the mind can take cogniz- 
ance of. and compare them. 

That a certain force of impulse and a certain time for its 
continuance are necessary to produce an audible impression 
on the ear, is evident, but it may be doubted whether the 
impression of a sound on this organ is retained appreciably 
longer than the continuance of the impulse itself, certainly 
it is not retained the ■j'^th of a second. If this were the case 
it is difficult to conceive why articulated discourse, which so 
pre-eminently distinguishes man from the lower animals, 
should not fill the ear with a monotonous hum; but whether 
the ear continues to vibrate, or whether the impression re- 



408 WRITINGS OP JOSEPH HENBT. [1856 

mains a certain time on the sensorium, it is certain that no 
sound is ever entirely instantaneous, or the result of a single 
impression, particularly in enclosed spaces. The impulse is 
not only communicated to the ear but to all bodies around, 
which in turn become themselves centres of reflected im- 
pulses. Every impulse must give rise to a forward and 
afterward a backward motion of a small portion of the 
medium. 

Sound from a single explosion in air equally elastic on 
all sides tends to expand equally in every direction ; but 
when the impulse is given to the air in a single direction, 
though an expansion takes place on all sides, yet it is much 
more intense in the line of the impulse. For example, the' 
impulse of a single -explosion, like that of the detonation of 
a bubble of oxygen and hydrogen, is propagated equally in 
all directions, while the discharge of a cannon, though heard 
on every side, is much louder in the direction of the axis; 
80 also a person speaking is heard much more distinctly 
directly in front than at an equal distance behind. Many 
experiments have been made on this point, and I may men- 
tion those repeated in the open space in front of the Smith- 
sonian Institution. In a circle 100 feet in diameter, the 
speaker in the centre, and the hearer in succession at differ- 
ent points of the circumference, the voice was heard most 
distinctly directly in front, gradually less so on either side, 
until in the rear it was scarcely audible. The ratio of dis- 
tance for distinct hearing directly in front, on the sides, and 
in the rear was about as 100, 75, and 30. These numbers 
may serve to determine the form in which an audience 
should be arranged in an open field in order that those on 
the periphery of the space may all have a like favorable 
opportunity of hearing, though such a disposition should 
not be recommended as the form of an apartment where a 
reflecting wall would be behind the speaker. 

The impulse producing sound requires time for its propa- 
gation, and this depends upon the intensity of repulsion 
between the atoms, and secondly, on the specific gravity of 
the matter itself. If the medium were entirely rigid sound 



410 WRITINGS OF JOSEPH HENRY. [1856 

longation of the sound was observed. By accurately meas- 
uring this distance and doubling it we find the interval of 
space within which two sounds may follow each other without 
appearing separately. But if two rays of sound reach the 
ear after having passed through distances the difference 
between which is greater than this, they produce the effect 
of separate sounds. This distance we have called the limit 
of perceptibility in terms of space. If we convert this distance 
into the velocity of sound, we ascertain the limit of percep- 
tibility in time. 

In the experiment first made with the wall a source of 
error was discovered in the fact that a portion of the sound 
returned was reflected from the cornice under the eavep, and 
as this was at a greater distance than the part of the wall 
immediately perpendicular to the observer the moment of 
cessation of the echo was less distinct. In subsequent ex- 
periments with a louder noise, the reflection was observed 
from a perpendicular surface of about 12 feet square, and 
from this more definite results were obtained. The limit of 
the distance in this case was about 30 feet, varying slightly 
perhaps with the intensity of the sound and the acuteness 
of different ears. This will give about the sixteenth part of 
a second as the limit of time necessary for the ear to sepa- 
rately distinguish two similar sounds. From this experi- 
ment we learn that the reflected sound may tend to strengthen 
the impression, or to confuse it, according as the difference 
of time between the two impressions is greater or less than 
the limit of perceptibility. An application of the same 
principle gives us the explanation of some phenomena of 
sound which have been considered mysterious. Thus, in 
the reflection of an impulse from the edge of a forest of trees 
each leaf properly situated within a range of 30 feet of the 
front plane of reflection will conspire to produce a distinct 
eclio, and these would form the principal part of the reflect- 
ing surfaces of a dense forest, for the remainder would be 
screened ; and being at a greater distance, any ray which 
might come from them would serve to produce merely a low 
continuation of the sound. 



412 WRITINGS OF JOSEPH HENRY. [1856 

at which the apparatus is placed, the second sound will com- 
bine with the first, and thus a loud and sustained vibra- 
tion will be produced. It will be evident from this that 
every room has a key-note, and that to an instrument of the 
proper pitch it will resound with great force. It must be 
apparent also, that the continuance of a single sound and 
the tendency to confusion in distinct perception, will depend 
on several conditions; — first, on the size of the apartment; 
secondly, on the strength of the sound or the intensity of 
the impulse; thirdly, on the position of the reflecting sur- 
faces; and fourthly, on the nature .of the material of the 
reflecting surfaces. 

In regard to the first of these, the larger the room the 
longer time will be required for the impulse along the axis 
to reach the wall; and if we suppose that at each collision a 
portion of the original force is absorbed, it will require 
double the time to totally extinguish it in a room of double 
the size, because, the velocity of sound being the same, the 
number of collisions in a given time will be inversely as 
the distance through which the sound has to travel. 

Again, that it must depend upon the loudness of the sound 
or the intensity of the impulse, must be evident, when we 
consider that the cessation of the reflections is due to the 
absorption by the walls, or to irregular reflection, and that 
consequently the greater the amount of original disturb- 
ance the longer will be the time required for its complete 
extinction. This principle was abundantly shown by our 
observations on different rooms. 

Thirdly, the continuance of the resonance will depend 
upon the position of the reflecting surfaces. If these are not 
parallel to each other, but oblique, so as to reflect the sound 
not to the opposite but to the adjacent wall, without passing 
through the longer axis of the room, it will evidently be 
sooner absorbed. Any obstacle, also, that may tend to break 
up tlie wave and interfere with the reflection through the axis 
of the room will serve to lessen the resonance of the apart- 
ment. Hence, though the panelling, the ceiling, and the 
introduction of a variety of oblique surfaces, may not pre- 



1856] WRITINGS OP JOSEPH HENRY. 413 

vent an isolated echo, provided the distance be sufficiently 
great and the sound sufficiently loud, yet that they do have 
an important effect in stopping the resonance is evident from 
theory and experiment. In a room 50 feet square in which 
the resonance of a single intense sound continued six seconds, 
when cases and other objects were placed around the wall its 
continuance was reduced to two seconds. 

Fourthly, the duration of the resonance will depend upon 
the nature of the material of the wall. A reflection always 
takes place at the surface of a new medium, and the amount 
of this will depend upon the elastic force or power to resist 
compression and the density of the new medium. For ex- 
ample, a wall of nitrogen, if such could be found, would 
transmit nearlv the whole of a wave of sound in air, and 
reflect but a very small portion; a partition of tissue-paper 
would produce nearly the same effect. A polished wall of 
steel however, of sufficient thickness to prevent yielding, 
would reflect for practical purposes all the impulses through 
the air which might fall upon it. The rebound of the wave 
is caused, not by the oscillation of the wall, but by the elas- 
ticity and mobility of the air. The striking of a single ray 
of sound against a yielding board would probably increase 
the loudness of the reverberation but not its continuance. 
On this point a series of experiments was made by the use 
of the tuning-fork. In this instrument the motion of the 
foot and of the two prongs gives a sonorous vibration to the 
air, which, if received upon another tuning-fork of precisely'' 
the same size and form, would re-produce the same vibra- 
tions. 

It is a fact well established by observation that when two 
bodies are in perfect unison, and separated from each other 
by a space filled with air, vibrations of the one will be taken 
up by the other. F-rom this consideration it is probable 
that relatively the siame eflbct ought to be produced in trans- 
mitting immediately the vibration of a tuning-fork to a 
reflecting body as to duration and intensity as in the case of 
transmission through air. This conclusion is strengthened 
by floating a flat piece of wood on water in a vessel standing 



414 WRITINGS OF JOSEPH HENRY, [1856 

upon a sounding-board; placing a tuning-fork on the wood 
the vibrations will be transmitted to the board through the 
water, and sounds will be produced of the same character as 
those emitted when the tuning-fork is placed directly upon 
the board. 

A tuning-fork suspended from a fine cambric thread and 
vibrated in air was found, from the mean of a number of 
experiments, to continue in motion 252 seconds. In this 
experiment, had the tuning-fork been in a perfect vacuum 
suspended without the use of a string, and further, had there 
been no CDtherial medium, the agitation of which would give 
rise to light, heat, electricity, or some other form of setherial 
motion, the fork would have continued its vibration for- 
ever. 

The fork was next placed upon a large, thin pine board — 
the top of a table. A loud sound in this case was produced 
which continued less than ten seconds. The whole table as 
a system was thrown into motion, and the sound produced 
was as loud on the under side as on the upper side. Had 
the tuning-fork been placed against a partition of this mate- 
rial a loud sound would have been heard in the adjoining 
room^ and this was proved by sounding the tuning-fork 
against a door leading into a closed closet. The sound 
within was apparently as loud as that without. 

TIic rapid decay of sound in this case was produced by so 
great an amount of the motive power of the fork being com- 
municated to a largo mass of wood. The increased sound 
was due to the increased surface. In other words the short- 
ness of duration was compensated for by the greater intensity 
of effect produced. 

The tuning-fork was next placed upon a circular slab of 
marble about three feet in diameter and three-quarters of an 
inch thick. The sound emitted was feeble, and the undula- 
tions continued one hundred and fifteen seconds, as deduced 
from the mean of six experiments. 

In all these experiments, except the one in a vacuum, the 
time of the cessation of the motion of the tuning-fork was 
determined by bringing the mouth of a resounding cavity 



1856] WRITINGS OP JOSEPH HENRY. 415 

near the end of the fork, this cavity having previously been 
adjusted to unison with the vibrations of the fork, gave an 
audible sound when none could be heard by the unaided 
ear. 

The tuning-fork was next placed upon a cube of India- 
rubber, and this upon the marble slab. The sound emitted 
by this arrangement was scarcely greater than in the case of 
the tuning-fork suspended from the cambric thread, and 
from the analogy of the previous experiments, we might at 
first thought suppose the time of duration would be great, 
but this was not the case. The vibrations continued only 
about forty seconds. The question may here be asked. What 
became of the impulses lost by the tuning-fork ? They were 
neither transmitted through the India-rubber nor given off 
to the air in the form of sound, but were probably expended 
in producing a change in the matter of the India-rubber, or 
were converted into heat, or both. Though the inquiry did 
not fall strictly within the line of this series of investigations, 
yet it was of so interesting a character in a physical point of 
view to determine whether heat was actually produced that 
the following experiment was made. 

A cylindrical piece of India-rubber about an inch and a 
quarter in diameter was placed in a tubulated bottle with 
two openings, one near the bottom and the other at the top. 
A stuffing-box was attached to the upper opening, through 
which a metallic stem with a circular foot to press upon the 
India-rubber was made to pass air-tight. The lower opening 
was closed with a cork, in a perforation of which a fine glass 
tube was cemented. A small quantity of red ink was placed 
in the tube to serve as an index. The whole arrangement 
thus formed a kind of air-thermometer, which would indicate 
a certain amount of change of temperature in the enclosed 
air. On the top of the stem the tuning-fork was screwed, 
and consequently its vibrations were transmitted to the rub- 
ber within the bottle. The glass was surrounded with several 
coatings of flannel to prevent the influence of external tem- 
perature. The tuning-fork was then sounded, and the vibra- 
tions were kept up for some time. No reliable indications 



416 WRITINOS OP JOSEPH HENRY. [1856 

of an increase of temperature were observed. A more deli- 
cate method of making the experiment next suggested itsell 
The tube containing the drop of red ink, with its cork, was 
removed, and the point of a compound wire formed of copper 
and iron was thrust into the substance of the rubber, while 
the other ends of the wire were connected with a delicate 
galvanometer. The needle was sufiFered to come to rest, the 
tuning-fork was then vibrated, and its impulses transmitted 
to the rubber. A very perceptible increase of temperature 
was the result. The needle moved through an arc of from 
one to two and a half degrees. The experiment was varied 
and many times repeated; the motions of the needle were 
always in the same direction, namely, in that which was 
produced when the point of the compound wire was heated 
by momentary contact with the fingers. The amount of heat 
generated in this way however is small, and indeed in all 
cases in which it is generated by mechanical means the 
amount evolved appears very small in comparison with the 
labor expended in producing it. Joule has shown that the 
mechanical energy generated in a pound weight by falling 
through a space of seven hundred and fifty feet elevates the 
temperature of a pound of water one degree. 

It is evident that an object like India-rubber actually 
destroys a portion of the sound, and hence in cases in which 
entire non-conduction is required this substance can prob- 
ably be employed with perfect success. 

The tuning-fork was next pressed upon a solid brick wall, 
and the duration of the vibration from a number of trials 
was eighty -eight seconds. Against a wall of lath and plaster 
the sound was louder and continued only eighteen seconds. 

From these experiments we may infer that if a room were 
lined with a wainscot of thin boards and a space left between 
the wall and the wood, the loudness of the echo of a single 
noise would be increased while the duration of the reson- 
ance would be diminished. If however the thin board were 
glued or cemented in solid connection to the wall, or em- 
bedded in the mortar, then the effect would be a feeble echo 
and a long continued resonance, similar to that from the 



1856] WRITINGS OF JOSEPH HENRY. 417 

slab of marble. This was proved by first determining the 
length of continuance of the vibrations of a tuning-fork on 
a thin board, which was afterwards cemented to a flat piece 
of marble. 

A series of experiments was next commenced with refer- 
ence to the actual reflection of sound. For this purpose a 
parabolic mirror was employed, and the sound from a watch 
received on the mouth of a hearing-trumpet furnished with 
a tube for each ear. The focus was near the apex of the 
parabola, and when the watch was suspended at this point 
it was six inches within the plane of the outer circle of the 
mirror. In this case the sound was confined at its origin, 
and prevented from expanding. No conjugate focus was 
produced, but on the contrary the rays of light, when a 
candle was introduced, constantly diverged. The ticking of 
the watch could not be heard at all when the ear was applied 
to the outside of the mirror, while directly in front it was 
distinctly heard at the distance of thirty feet, and with the 
assistance of the ear trumpet at more than double that dis- 
tance. When the watch was removed from the focus the 
sound ceased to be audible. This method of experimenting 
admits of considerable precision, and enables us to directly 
verify, by means of sound transmitted through air, the 
results anticipate in the previous experiments. A piece of 
tissue-paper placed within the mirror and surrounding the 
watch without touching it, slightly diminished the reflection. 
A single curtain of flannel produced a somewhat greater 
effect, though the reflecting power of the metallic parabola 
was not entirely masked by three thicknesses of flannel; and 
I presume very little change would have been perceived had 
the reflector been lined with flannel glued to the surface of 
the metal. The sound was also audible at the distance of 
ten feet when a large felt hat without stiffening was inter- 
posed between the watch and the mirror. Care was taken 
in these experiments so to surround the watch that no ray 
of sound could pass directly from it to the reflecting surface. 

With a cylindrical mirror, having a parabolic base, very 
little increased reflection was perceived. The converging 

27-2 



418 WRITINGS OF JOSEPH HENRY. [1856 

beams in this case were merely in a single plane, perpen- 
dicular to the mirror, and passing through the ear, while to 
the focal point of the spherical mirror a solid cone of rays 
was sent. 

The reflection from the cylindrical mirror forms what is 
called a caustic in optics, while that from a cylindrical mir- 
ror gives a true focus, or in other words collects the sounds 
from all parts of the surface and conveys them to one point 
of space. These facts furnish a ready explanation of the 
confusion experienced in the Hall of Representatives, which 
is surmounted by a dome, the under surface of which acts as 
an immense concave mirror, reflecting to a focus every sound 
which ascends to it, leaving other points of space deficient 
in sonorous impulses. 

Water, and all liquids which offer great resistance to com- 
pression, are good reflectors of sound. This may be shown 
by the following experiment. When water is gradually 
poured into an upright cylindrical vessel, over the mouth of 
which a tuning-fork is vibrated, until it comes within a 
certain distance of the mouth, it will reflect an echo in 
unison with the vibration of the fork, and produce a loud 
resonance. This result explains the fact, which had been 
observed with some surprise, that the duration of the reson- 
ance of a newly plastered room was not perceptibly less than 
that of one which had been thoroughly dried. 

There is another principle of acoustics which has a bear- 
ing on this subject. I allude to the refraction of sound. It 
is well known that when a ray of sound passes from one 
medium to another a change in velocity takes place, and 
consequently a change in the direction or a refraction must 
bo produced. The amount of this can readily be calculated 
where the relative velocities are known. In rooms heated 
by furnaces, and in which streams of heated air pass up 
between the audience and speaker, a confusion has been 
supposed to be produced and distinct hearing interfered with 
by this cause. Since the velocity of sound in air at 32° of 
Fahrenheit lias been found to been 1090 feet in a second, 
and since the velocity increases 114 feet for every degree of 



1856] WRITINGS OF JOSEPH HENRY. 419 

Fahrenheit's scale, if we know the temperature of the room 
and that of the heated current the amount of angular refrac- 
tion can be ascertained. But since the ear does not readily 
judge of the difference of direction of two sounds emanating 
from the same source, and since two rays do not confuse the 
impression which they produce upon the ear though they 
arrive by very different routes, provided they are within 
the limit of perceptibility, we may conclude that the in- 
distinctness produced by refraction is comparatively little. 
Professor Bacho and myself could perceive no difference in 
distinctness in hearing, from rays of sound passing over a 
chandelier of the largest size in which a large number of 
gas jets were in full combustion. The fact of disturbance 
from this cause however, (if any exist,) may best be deter- 
mined by the experiment with a parabolic mirror and the 
hearing-trumpet before described. 

These researches might be much extended; they open a 
field of investigation equally interesting to the lover of 
abstract science and to the practical builder; and I hope, on 
behalf of the committee, to give some further facts with 
regard to this subject at another meeting. 

Tfie Smithsonian Leciure-room. — I shall now briefly describe 
the lecture-room of the Smithsonian Institution, which has 
been constructed in accordance with the facts and principles 
previously stated, so far at least as they could be applied. 

There was another object kept in view in tJie construc- 
tion of this room besides the accurate hearing, namely the 
distinct seeing. It was desirable that every person should 
have an opportunity of seeing the experiments which might 
be performed, as well as of distinctly hearing the explanation 
of them. 

By a fortunate co-incidence of principles, it happens that 
the arrangements for insuring unobstructed sight do not 
interfere with those necessary for distinct hearing. 

The law of Congress authorizing the establishment of the 
Smithsonian Institution directed that a lecture-room should 
be provided; and accordingly in the first plan one-half of 
the first story of the main building was devoted to this pur- 



420 WRITINGS OF JOSEPH HENRY. [1856 

pose. It was found impossible however to construct a room 
on acoustic principles in this part of the building, which was 
necessarily occupied by two rows of columns. The only 
suitable place which could be found was therefore on the 
second floor. The main building is two hundred feet long 
and fifty feet wide; but by placing the lecture room in the 
middle of the story a greater width was obtained by means 
of the projecting towers. 

The main gallery is in the form of a horse-shoe occu- 
pying three sides of the room. The speaker's platform is 
placed between two oblique walls. The corners of the room 
which are cut off by these walls afford recesses for the stairs 
into the galleries. The opposite corners are also partitioned 
off so as to afford recesses for the same purpose. ' 

The general appearance of the room is somewhat fan- 
shaped, and the speaker is placed in the mouth as it were 
of an immense trumpet. The sound directly from his voice 
and that from reflection immediately behind him is thrown 
forward upon the audience; and as the difference of distance 
travelled by the two rays is much within the limit of per- 
ceptibility no confusion is produced by direct and reflected 
sound. 

Again, on account of the oblique walls behind the speaker 
and the multitude of surfaces, including the gallery, pillars, 
stair-screens, &c., as well as the audience, directly in front, 
all reverberation is stopped. 

The walls behind the speaker are composed of lath and 
plaster, and therefore have a tendency to give a more intense 
though less prolonged sound than if of solid masonry. 
They are also intended for exhibiting drawings to the best 
advantage. 

The seats are arranged in curves and were intended to rise 
in accordance with the panoptic curvey originally proposed by 
Professor Bacho, which enables each individual to see over 
the head of the person immediately in front of him. The 
original form of the room however did not allow of this 
intention being fully realized, and therefore the rise is some- 
what less than the curve would indicate. 



1856] WRITINGS OP JOSEPH HENRY. 421 

The ceiling is twenty-five feet high, and therefore within 
the limit of perceptibility. It is perfectly smooth isind un- 
broken with the exception of an oval opening nearly over 
the speaker's platform through which light is admitted. 

No echo is given oflf from the ceiling, while this assists the 
hearing in the gallery by the reflection to that place of 
the oblique rays. 

The architecture of this room is due to Captain B. S. 
Alexander, of the corps of Topographical Engineers. He 
fully appreciated all the principles of sound which I have 
given, and varied his plans until all the required conditions 
as far as possible were fulfilled. 



ACXX)UNT OP A LARGE SULPHURIC-ACID BAROMETER IN THE 
HALL OP THE SMITHSONIAN INSTITUTION. 

(Proceedings American Association Adv. of Science, vol. x, pp. 135-138.) 

August 23, 1856. 

The opinion has been frequently advanced thata barom- 
eter in which the material used to balance the pressure of 
the atmosphere is of less specific gravity than mercury, and 
consequently of a wider range of fluctuation, might throw 
some new light on several important points of peteorology. 
The fluid usually proposed for this purpose has been oil or 
water, the viscid character of the former and its tendency 
to a change of condition has induced a preference for the 
latter. Several water-barometers have accordingly been con- 
structed; but as far as I am informed, the indications of the 
instruments have not been reliable. 

Mariotte used one of this character ; also Otto von Guericke 
constructed a philosophical toy to which he gave the name 
of aeroscope, on the principle of a water-barometer. It 
consisted of a tube more than thirty feet high elevated on a 
long wall and terminated by a tall and rather wide glass 
cylinder hermetically sealed, in which was placed a toy in 
the shape of a man. All the tube except a portion of 



4?2 WRITINGS OP JOSEPH HENRT. . [1856 

the cylindrical part was concealed behind the wainscoting, 
and consequently the little image made its appearance only 
in fine weather. 

A water-barometer was constructed by Professor Daniell, 
and placed in the hall of the Royal Society, of which a full 
account has been published in the Transactions of that insti- 
tution. A minute account is given of the method of blowing 
the tube, and the details of permanently fastening it in the 
box which was to form the case. The tube was left open at 
both ends ; to the upper one a stop-cock was attached, and 
the lower one was inserted in a small steam boiler, which 
served the purpose of boiling the water to expel all the air, 
of elevating it to the proper height by means of the elastic 
force of the steam, and also as a permanent cistern to the 
barometer. After the water was forced to the top and issued 
from the stop-cock in a jet, the latter was closed ; the stop- 
cock in the boiler was opened, steam suffered to escape, and 
the water to settle in the tube until balanced by the pressure 
of air. The upper part of the glass under the stop-cock, 
(which had previously been drawn out into a fine tube,) was 
gradually heated by a blow-pipe, and as soon as it was suffi- 
ciently softened the pressure of the air effectually closed it. 
The part above the stop-cock was then removed with a file. 
This barometer was completed, after adjusting the scale, by 
pouring a quantity of castor-oil on the surface of the water 
to prevent contact with the air. 

After a series of observations however it was found in the 
course of about three months that the column of water was 
gradually descending, and it was finally resolved to open the 
boiler and to examine the instrument. The oil upon the sur- 
face was found to have undergone a change, though the water 
below was perfectly bright and transparent. A portion of . 
the water was taken out and placed under the receiver of 
an air-pump, and bubbles of air in abundance were extri- 
cated; the air was absorbed by the water, diffused through 
the whole mass to the top, where it was given off to the 
vacuum, and thus caused the gradual descent of the column. 
It was found however that it was not atmospheric air in the 



1856] WRITINGS OF JOSEPH HENRY. 423 

vacuum, but nearly pure nitrogen: the oxygen had been 
absorbed in passing through the oil, producing rancidity 
and other changes in that liquid. 

It was evident from this experiment that oil was not im- 
pervious to air. Another attempt to remedy this defect of 
the instrument was made by using a thin film of gutta- 
percha, to be left after the evaporation of tlie naptha in 
which it had been dissolved. 

An objection however to the use of water as the liquid for 
the barometer is the vapor which it always gives oflf, and of 
which the tension cannot readily be determined. In a glass 
vessel in which a cup of water is enclosed. Professor Espy 
informs me that he has found the dew-point always less than 
that which would be due to the temperature. 

Desiring to fit up a barometer on a large scale as one of the 
objects of interest and use in the Smithsonian Institution, 
I consulted my friend Professor G. C. SchaeflTer of the Patent 
OflBce, as to the best liquid to be employed. He advised the 
use of sulphuric acid, but I did not immediately adopt his 
advice on account of the apparently dangerous character of 
this substance. Happening however some time afterwards 
to be speaking on the subject of barometers with Mr. James 
Green, the instrument- maker, in the presence of Professor 
Ellet, of New York, the latter asked why I did not have a 
large one constructed with sulphuric acid. The suggestion 
having thus again been independently made, and Mr. Green 
expressing his willingness to undertake the work, I gave the 
order for the construction of the instrument, and requested 
Professor Ellet to give any suggestions as to the details 
which might be required. 

The advantages of this liquid are: 1. That it gives oflf no 
appreciable vapor at any atmospheric temperature; and 2. 
That it does not absorb or transmit air. The objections to 
its use are: 1. The liability to accident from the corrosive 
nature of tlie liquid, either in the filling of the tube or in its 
subsequent breakage; and 2. Its aflBnity for moisture, which 
tends to produce a change in specific gravity. The filling 
however is a simple process and attended with but little if 



424 WRITINGS OF JOSEPH HENRY' [1856 

any risk. The acid can gradually be poured into the tube 
while in its case, slightly inclined to the horizon. Any 
accident from breakage can be prevented by properly secur- 
ing the whole instrument in an quter case, which will also 
serve to equalize the temperature. To prevent the absorp- 
tion of moisture the air may be previously passed through 
a drying tube apparatus. The only point in which water 
would be preferable to sulphuric acid is the less specific 
gravity of the former, and consequently the greater range of 
its fluctuation, which is as 20 : 11, nearly. 

The general appearance of the instrument and the several 
contrivances for adjustment and reading are in accordance 
with the reputation of the skillful and intelligent artizan who 
made it. The glass tube is two hundred and forty inches 
long and three-fourths of an inch in diameter, and is en- 
closed in a cylindrical brass case of the same length, and 
two and a half inches in diameter. The glass tube is secured 
in the axis of the brass case by a number of cork collars 
placed at intervals; which, while they prevent all lateral 
displacement of the tube, allow it to be moved upward and 
downward for the adjustment of the zero-point. 

The reservoir consists of a cylindrical glass bottle of four 
inches in diameter with two openings at the top; one in the 
axis to admit the lower end of the long tube, which is 
tapered to about one-half of the general diameter, the other 
to transmit the varying pressure of the atmosphere. 

To adjust the zero-point the whole glass part of the appa- 
ratus together with the contained acid is elevated or de- 
pressed by a screw placed under the bottom, uhtil the level 
of the acid in the reservoir coincides with a fixed mark. 

The scale for reading the elevation is divided into inches 
and tenths, and by means of a vernier, moved by a rack and 
pinion, the variations can be measured to the hundredth of 
an inch, and estimated to a still smaller division. 

The vernier itself is not immediately attached to the 
cylindrical brass case, but to a sliding frame which can be 
moved along the whole opening through which the entire 
range of the column is observed. The motion of the frame 



1856] WRITINGS OP JOSEPH HENRY. 425 

enables us to make the first rough adjustment, and that of 
the rack and pinion the minute one. 

The drying apparatus, placed between the external air 
and the interior of the reservoir, consists of a tubulated bot- 
tle (with two openings) containing chloride of calcium, and 
connected with the reservoir by an India-rubber tube ; by 
which arrangement the air is deprived of its moisture. 

To ascertain the temperature of the column of the liquid 
two thermometers are attached, one at the top and the other 
near the bottom. 

The whole apparatus is enclosed in an outer glazed case 
of twelve inches square, which serves (as mentioned before) 
as well for protection as for equalizing the temperature, 
which is ascertained with sufficient accuracy by taking the 
mean of the two thermometers. 

A large correction is required in this barometer for the 
expansion and contraction by the changes of temperature. 
To determine the amount of this, the specific gravity of a 
quantity of the acid with which the barometer had been 
filled was taken at different temperatures. This process was 
performed with a very sensitive balance, by Dr. Easter, in 
the laboratory of the Institution. 



426 WRmxGS of Joseph henrt. [1857 



STATEMENT IN RELATION TO THE HISTORY OP THE ELECTRO- 
MAGNETIC TELEGRAPH.* 

(From the Smithsonuin Annual Report for 1857, pp. 9^106.) 

A series of controversies and law suits having arisen be- 
tween rival claimants for tel^raphic patents, I was repeatedly 
appealed to to act as expert and witness in such cases. This 
I uniformly declined to do, not wishing to be in any manner 
involved in these litigations; but I was finally compelled 
under legal process to return to Boston from Maine — ^whither 
I had gone on a visit, and to give evidence on the subject 
My testimony was given with the statement that I was not a 
willing witness, and that I labored under the disadvantage 
of not having access to my notes and papers, which were in 
Washington. 

In the beginning of my deposition I was requested to give 
a sketch of the history of electro-magnetism having a bearing 
on the telegraph, and the account I then gave from memory I 
have since critically examined, and find it fully corroborated 
by reference to the original authorities. My sketch, which 
was the substance of what I had been in the habit of giving 
in my lectures, was necessarily very concise, and almost 
exclusively confined to one class of facts, namely, those hav- 
ing a direct bearing on Mr. Morse's invention. In order 
therefore to set forth more clearly in what my own improve- 
ments consisted, it may be proper to give a few additional 
particulars respecting some points in the progress of discov- 
ery, illustrated by wood cuts. 

There are several forms of the electrical telegraph ; first, 
that in which frictional electricity has been proposed to pro- 
duce sparks, and motion of pith balls at a distance. 

Second, that in which galvanism has been employed to 
produce signals by means of bubbles of gas from the decom- 
position of water ; or by other chemical re-action. 

* [Presented to the Board of Regents of the Smithsoniun Institution, on 
their investigation (by a special committee) of certain publications touching 
the origin of the electro-magnetic telegraph.] 



18571 WRITINGS OF JOSEPH HENRY. 427 

Third, that in which electro-magnetism is the motive 
power to produce motion at a distance: and again, of the 
latter there are two kinds of telegraphs, those in which the 
intelligence is indicated by the motion of a magnetic needle 
and those in which sounds and permanent signs are made 
by the attraction of an electro-magnet. The latter is the 
class to which Mr. Morse's invention belongs. The follow- 
ing is a brief exposition of the several steps which led to 
this form of the telegraph : 

The first essential fact (as I stated in my testimony) that 
rendered the electro-magnetic telegraph possible was discov- 
ered by Oersted, in the winter of 1819-20. It is illustrated 
by figure 1, in which the magnetic needle is deflected by the 




Fig. 1. 

action of a current of galvanism transmitted through the 
wire A B. (See Annals of Philosophy^ Oct, 1820, vol. xvi, 
page 274.) 

The second fact of importance, discovered in 1820 by 
Arago and Davy, is illustrated in figure 2. It consists in 




Fig. 2. 

this, that while a current of galvanism is passing through a 
copper wire A B, it is quasi magnetic, that is, it attracts iron 
filings in a cylindrical sheath around it, and not those of 
copper or brass, developing magnetism in soft iron. (See 
Annalcs de Chimie et de Physique, 1820, vol. xv, page 94.) 

The next important discovery, also made in 1820, by 
Ampere, was that two wires through which galvanic currents 
are passing in the same direction attract — and in the oppo- 
site direction repel each other. On this fact Amp6re founded 



428 WRITINGS OF JOSEPH HENRY. [1857 

his celebrated theory that magnetism consists merely in the 
attraction of electrical currents revolving at right angles to 
the line joining the two poles of the magnet. The magnet- 
ization of a bar of steel or iron, according to this theory, 
consists in establishing within the metal by induction — a 
scries of electrical currents, all revolving in the same direc- 
tion at right angles to the axis or length of the bar. 

It was this theory which led Arago, as he states, to adopt 
the method of magnetizing sewing needles and pieces of 
steel wire shown in figure 3. This method consists in trans- 




FiG. 8. 

mitting a current of electricity through a helix surrounding 
the needle or wire to be magnetized. For the purpose of 
insulation the needle was inclosed in a glass tube, and the 
several turns of the helix were at a distance from each other 
to insure the passage of electricity through the whole length 
of the wire, or in other words, to prevent it from seeking a 
shorter passage by cutting across from one spire to another. 
The helix employed by Arago obviously approximates the 
arrangement required by the theory of Ampere in order to 
develop by induction the magnetism of the iron. By an 
attentive perusal of the original account of the experiments 
of Arago (given in the Annales de Chimie d Physique, 1820, 
vol. XV, pages 93-95) it will be seen that properly speaking he 
made no electro-magnet, as has been often stated. His ex- 
periments were confined to the magnetizing of iron filings, 
sewing needles, and pieces of steel wire of the diameter of a 
millimetre, or of about the thickness of a small knitting 
needle. 

Mr. Sturgeon, in 1825, made an important step in advance 
of the experiments of Arago, and produced what is properly 
known as the electro-magnet. lie bent a piece of iron wire 
into the form of a horseshoe, covered it with varnish to insu- 
late it, and surrounded it with a helix, of which the spires 
were at a distance. When a current of galvanism was 




1857] WRITINGS OP JOSEPH HENRY. 429 

passed through the helix from a small battery of a single 
cup the iron wire became magnetic, and continued so during 
the passage of the current. When the current was inter- 
rupted the magnetism disappeared, and thus was produced 
the first temporary soft iron magnet. 

The electro-magnet of Sturgeon 
is shown in figure 4, which is a 
copy from the drawing in the Trans- 
actioyis of the Society for the Encourage- 
ment of Arts, &c., 1825, vol. xliii, pp. 
38-52. By comparing figures 3 and 
4, it will be seen that the helix em- 
ployed by Sturgeon was of the same Fig. 4. 
kind as that used by Arago; instead of a straight steel wire 
inclosed in a tube of glass however. Sturgeon employed a 
bent wire of soft iron. The difference in the arrangement at 
first sight might appear to be small, but the difierencc in the 
results produced was important, since the temporary magnet- 
ism developed in the arrangement of Sturgeon wa? suflicient 
to support a weight of several pounds; and an instrument 
was thus produced of value in future research. 

The next improvement was made by myself. After read- 
ing an account of the galvanometer of Schweigger, the idea 
occurred to mo that a much nearer approximation to the 
requirements of the theory of Ampere could be attained by 
insulating the conducting wire itself, instead of the rod to be 
magnetized, and by covering the whole surface of the iron 
with a series of coils in close contact. This was effected by 
insulating a long wire with silk thread, and winding this 
around the rod of iron in close coils from one end to the 

n other. The same principle was extended by 
employing a still longer insulated wire, and 
winding several strata of this over the first, 
care being taken to insure the insulation be- 
tween each stratum by a covering of silk 
ribbon. By this arrangement the rod was sur- 
Fio. 5. rounded by a compound helix formed of a 
long wire of many coils, instead of a single helix of a few 
coils. (Fig. 5.) 



430 WRITINGS OF JOSEPH HENRY. [1857 

In the arrangement of Ara^ and Sturgeon the several 
turns of wire were not precisely at right angles to the axis 
of the rod, as they should be — to produice the effect required 
by the theory, but slightly oblique, and therefore each 
tended to develop a separate magnetism not coincident with 
the axis of the bar. But in winding the wire over itself, the 
obliquity of the several turns compensated each other, and 
the resultant action was at right angles to the bar. The 
arrangement then introduced by myself was superior to 
those of Arago and Sturgeon, first in the greater multiplicity 
of turns of wire, and second in the better application of these 
turns to the development of magnetism. The power of the 
instrument, with the same amount of galvanic force, was by 
this arrangement several times increased. 

The maximum effect however with this arrangement and 
a single battery was not yet obtained. After a certain length 
of wire had been coiled upon the iron, the power diminished 
with a further increase of the number of turns. This was 
due to the increased resistance which the longer wire offered 
to the conduction of electricity. Two methods of improve- 
ment therefore suggested themselves. The first consisted — 
not in increasing the length of the coil, but in using a num- 
ber of separate coils on the same piece of iron. By this 
arrangement the resistance to the conduction of the elec- 
tricity was diminished, and a greater quantity made to cir- 
culate around the iron from the same battery. The second 
method of producing a similar result consisted in increasing 
the number of elements of the battery, or in other words 
the projectile force of the electricity, which enabled it to 
pass through an increased number of turns 
of wire, and thus by increasing the length 
of the wire, to develop the maximum power 
of the iron. 

To test these principles on a larger scale, 
the experimental magnet was constructed, 
which is shown in figure 6. In this a num- 
ber of compound helices was placed on the FiQ- 6. 
same bar, their ends left projecting, and so numbered that 




432 WRITINGS OP JOSEPH HENRT. [1857 

ma^etic machiocs which have since exercised the inge- 
nuity of inventors in ever/ part of the world, and were of im- 
mediate applicability in the introduction of the magnet to 
lelegraphic purposes. Neither the electro-magnet of Sturgeon 
nor any electro-magnet ever made previous to my investiga- 
tions was applicable to transmitting power to a distance. 

The principles I have developed were properly appreci- 
ated by the scientific mind of Dr. Gale, and applied by him 
(o operate Mr. Morse's machine at a distance.f 

Previous to my investigations the means of developing 
magnetism in soft iron were imperfectly understood. The 
electro-magnet made by Sturgeon, and copied by Dana, of 
New York, was an imperfect quantity magnet, the feeble 
power of which was developed b}' a single battery. It was 
entirely inapplicable to a long circuit with an intensity bat- 
ter}', and no person possessing the requisite scientific knowl- 
edge, would have attempted to use it in that connection 
after reading my. paper. 

In sending a message to a distance, two circuits are em- 
ployed, the first a long circuit through which the electricity 
is sent to the distant station to bring into action the second — 
a short one, in which is the local battery and magnet for 
working the machine. In order to give projectile force suf- 
ficient to send the power to a distance, it is necessary to use an 
intensity battery in the long circuit; and in connection with 
this at the distant station a magnet surrounded with many 
turns of one long wire must be employed to receive and 
multiply the effect of the current enfeebled by its transmis- 
sion through the long conductor. In the local or short cir- 
cuit either an intensity or quantity magnet may be employed. 
If the first be used, then with it a compound battery will bo 
required ; and therefore on account of the increased resist- 
ance due to the greater quantity of acid, a less amount of 
work will be performed by a given amount of material; and 
consequently though this arrangement is practicable it is by 
no means economical. In my original paper I state that the 
advantages of a greater conducting power, from using sev- 

f [Seo Appendix A, at the end of this paper.] 



1857} WRITINGS OF JOSEPH HENRY. 433 

eral wires in the quantity magnet may in a less degree be 
obtained by substituting for them one large wire; but in this 
case, on account of the greater obliquity of the spires and 
other causes, the magnetic effect would be less. In accord- 
ance, with these principles, the receiving magnet, or that 
which is introduced into the long circuit, consists of a horse- 
shoe magnet surrounded with many hundred turns of a 
single long wire, and is operated with a battery of from 12 
to 24 elements or more, while in the local circuit it is cus- 
tomary to employ a battery of one or two elements with a 
much thicker wire and fewer turns. 

It will I think be evident to the impartial reader that 
these were improvements in the electro-magnet which first 
rendered it adequate to the transmission of mechanical 
power to a distance; and had I omitted all allusion to the 
telegraph in my paper, the conscientious historian of science 
would have awarded me some credit, however small might 
have been the advance that I had made. Arago, and Stur- 
geon, in the accounts of their experiments, make no mention 
of the telegraph, and yet their names always have been and 
will be associated with the invention. I briefly called atten- 
tion however to the fact of the applicability of my experi- 
ments to the construction of the telegraph ; but not being 
familiar with the history of the attempts made in regard to 
this invention, I called it "Barlow's project," while I ought 
to have stated that Mr. Barlow's investigation merely tended 
to disprove the possibility of a telegraph. 

I did not refer exclusively to the needle telegraph when 
I stated in my paper that "the magnetic action of a current 
from a trough is at least not sensiblj^ diminished by passing 
through a long wire." This is evident from the fact that the 
immediate experiment from which this deduction was made, 
was by means of an electro-magnet and not by means of a 
needle galvanometer. 

' At the conclusion of the series of experiments which I 
described in Silliman's Journal, there were two applications 
of the electro-magnet in my mind: one, the production of a 
machine to be moved by electro-magnetism, and the other, 

28-2 



^^c 



434 WHITINGS OF iOSEPU UKN'RY. £US7 

tlic transiDJasion of or calling into action i>owcr at a distance. 
Tliu lirsl van carried into execution in the construction of 
the machine described in Silliinan's Journal in 1831 ;* and 
for the purjtose of experimenting in regard to the second, I 
arranged around one of the upper rooms in the Albany 

^ Academy a wire of more than 

a mile in length, through which 
I was enabled to make signals 
by sounding a bell. (Fig. 7.) 
^^^ The mechanical arrangement 
^^^^^f9 for effecting this object was 
_ simply a steel bar.penuanently 
» magnetized, of about ten incbes 
- in length, supported on a pivot, 
*'"■ '■ and placed with its north end 

txttwcen the two arras of a horse-shoe magnet. When the 
latter was excited by the current, the end of the bar thus 
placed was attracted by one arm of the horse-shoe, and 
repelled by the other, and was thu» caused to move in a 
horizontal plane and its further extremity to strike a bell 
suitably adjusted. 

This arrangement is that which is alluded to in Professor 
Hall's lettert as having been exhibited to him in 1832. It 
was not however at that time connected with the long wire 
above-mentioned, but with a shorter one put up around the 
room for exhibition. 

At the time of giving my testimony I was uncertain as to 
when I had first exhibited this contrivance, but have since 
definitely settled the fact by the testimony of Hall and others 
that it was before I left Albany, and abundant evidence can 
be brought to show that previous to my going to Princeton 
jn November, 1S32, my mind was much occupied with the 
subject of the telegraph, and that I introduced it in my 
course of instruction to the senior class in the Academy. I 

•[Sillimaa's American Jouroal of Science, July, 1831, vol. xx, pp. 
340-343. Spc aiile, vol. I, p. W] 

f [See -Ippcndii B, nt tbe end of this paper; anJalso Proceedings of tha 
Albany Institute, January IS, 18-38; vol. iv, pp. 244, 245.] 



1857] WRITINGS OF JOSEPH HENRY. 435 

should state however that the arrangement I have described 
was merely a temporary one, and that I had no idea at the 
time of abandoning my researches for the practical applica- 
tion of the telegraph. Indeed, my experiments on the 
transmission of power to a distance were suspended by 
the investigation of the remarkable phenomena (which I 
had discovered in the course of these experiments) of the 
induction of a current in a long wire on itself, and of which 
I made the first mention in a paper in Silliman's Journal 
in 1832.* 

I also devised a method of breaking a circuit and thereby 
causing a large weight to fall. It' was intended to illustrate 
the practicability of calling into action at a distance a great 
power capable of producing mechanical effects; but as a 
description of this was not printed, I do not place it in the 
same category with the experiments of which I published an 
account, or the facts which could be immediately deduced 
from my papers in Silliman's Journal. 

From a careful investigation of the history of electro- 
magnetism in its connection with the telegraph, the follow- 
ing facts may be established : 

r. Previous to my investigations the means of developing 
magnetism in soft iron were imperfectly understood, and 
the electr6- magnet which then existed was inapplicable to 
the transmission of power to a distance. 

2. I was the first to prove by actual experiment that in 
order to develop magnetic power at a distance a galvanic bat- 
tery of "intensity" must be employed to project the current 
through the long conductor, and that a magnet surrounded 
by many turns of one long wire must be used to receive this 
current. 

3. I was the first to actually magnetize a piece of iron at 
a distance, and to call attention to the fact of the applica- 
bility of my experiments to the telegraph. 

4. I was the first to actually sound a bell at a distance by 
means of the electro-magnet. 

* [Silliman's American Journal of Science, July, 1832, vol. xxii, p. 408. 
See aniCf vol. i, p. 79.] 



436 WRITINGS OF JOSEPH HENRY. [1857 

5. The principles I had developed were applied by Dr. 
Gale to render Morse's machine effective at a distance. 

The results here given were among my earliest experi- 
ments: in a scientific point of view I considered them of 
much less importance than what I subsequently accom- 
plished; and had I not been called upon to give my testi- 
mony in regard to them, I would have suffered them to 
remain (without calling public attention to them) a part of 
the history of science to be judged of by scientific men who 
are the best qualified to pronounce upon their merits. 



Appendix A. — Lftier from Dr. Oale. 

Washington, D. C, April 7, 1856. 

Sir: In roply to your note of the 3d instant, reipecting the Morse tele- 
graph, askin!^ me to state definitely the condition of the invention when I 
llrst saw the apparatus in the winter of 1836, I answer: This apparatus was 
Morse's original instrument, usually known as the typo apparatus, in which 
the types, set up in a composing stick, were run through a circuit hreaker, 
and in which the hatter}' was the cylinder hattery, with a single pair of 
plates. This arrangement also had another peculiarity, namely, it was the 
electro-magnet used hy Sturgeon, and shown in drawings of the older works 
on that suhject, having only a few turns of wire in the coil which surrounded 
the poles or arms of the magnet. The sparseness of the wires in the magnet 
coil< and the use of the single cup battery were to me, on the first look at 
iho instrument, obvi<»us marks of defect, and I accordingly suggested to the 
pn^fessor, without giving my rciisons for so doing, that a battery of many 
pairs should be substituted for that of a single pair, and that the coil on each 
arm of the magnet should be increased to many hundred turns each ; which 
experiment, if I remenibor aright, was made on the same day with a battery 
and wire on hand, (furnished I believe by myself,) and it was found that 
while the original arrangement would only send the electric current through 
a few feet of wire, say 1*5 to 10, the modified arrangement would send it 
through as many hundred. Although I gave no reason at the time to Pro- 
fessor Morse for the suggestions I had proposed in modifying the arrange- 
ment of the machine, I did so afterwards, and referred in my explanations to 
the paper of Professor Henry, in the 19th volume of the American Journal 
of Science, page 400 and onward. It was to these suggestions of mine that 
Professor Morse alludes in his testimony before the Circuit Court for the 
eastern district of Pennsylvania, in the trial of B. B. French and others r«. 
Rogers and others. See printed copy of complainant's evidence, page 168, 
beginning with the words, " Early in 1836 I procured 40 feet of wire," &c., 
and page 169, where Professor Morse alludes to myself and compensation, 
for services rendered to him, &c. 

At the time I gave the suggestions above named, Professor Morse was 



1857] WRITINGS OF JOSEPH HENRY. 437 

not familiar with the then existing state of the science of electro-magnetism. 
Had he been so, or had he read and appreciated the paper of Henry, the sug- 
gestions made by me would naturally have occurred to his mind as they did 
to my own. But the principal part of Morse's great invention lay in the 
mechanical adaptation of a power to produce motion, and to increase or relax 
at will. It was only necessary for him to kn^w that such a power existed for 
him to adapt mechanism to direct and control it. 

M}' suggestions were made to Professor Morse from inferences drawn by 
reading Professor Henry 's paper above alluded to. Professor Morse professed 
great surprise at the contents of the paper when I showed it to him, but 
especially at the remarks on Dr. Barlow's results respecting telegraphing, 
which were new to him; and he stated at the time that he was not aware 
that any one had even conceived the idea of using the magnet for such pur- 
poses. 

With sentiments of esteem, I remain, yours truly, 

L. D. Gale. 

Prof. Joseph Henry. 



Appendix B. — Letier from Prof. Hall. 

Albany, N. Y., January 19, 1856. 

Dear Sir : While a student of the Rensselaer School, in Troy, New 
York, in August, 1882, I visited Albany with a friend, having a letter of 
introduction to you from Professor Eaton. Our principal object was to see 
your electro-magnetic apparatus, of which we had heard much, and at the 
same time the library and collections of the Albany Institute. 

You showed us your laboratory in a lower story or ba.-ementof the build- 
ing, and in a larger room in an upper story some electric and galvanic ap- 
paratus, with various philosophical instruments. In this room, and extend- 
ing around the same, was a circuit of wire stretched along the wall, and at 
one termination of this, in the recess of a window, a bell waj fixed, while the 
other extremity was connected with a galvanic apparatus. 

You showed us the manner in which the bell could be made to ring by a 
current of electricity, transmitted through this wire, and you remarked that 
this method might be adopted for giving signals, by the ringing of a bell at 
the distance of man}' mile.s from the point of its connection with the galvanic 
apparatus. 

All the circumstances attending this visit to Albany are fresh in my re- 
collection, and during the past years, while so much has been said respect- 
ing the invention of electric telegraphs, I have often had occasion to mention 
the exhibition of your electric telegraph in the Albany Academy, in 1832. 

If at any time or under any circum^ttances this statement can be of service 

to you in substantiating your claim to such a discovery at the period named, 

you are at liberty to use it in any manner you please, and I shall be ready 

at all times to repeat and sustain what I have hero stated, with many other 

attendant circumstances, should they prove of any importance. 

I remain, very sincerely and respectfully, yours, 

James Hall. 
Professor Joseph Henry. 



T.iTTNGS or JOSEPH HENRY. [1859 



■:v THX \??Li«:Ar:*>N of the telegraph to the premoni- 

r: >y of weather changes. 

?^.o-— 1.0:1* Axtr^ai A ani-iny :-f An* And Sciences, vol. iv, pp. 271-275.) 

rr:«^T*=*:r Hrr^ry mi»ie a verbal commuuication relative 

-: '.'zji ircLi-ran*:-:: of the telegraph to the prediction of 

^M-i-:* -(f :h-r wr:i:hvr. particularly in the city of Boston 

I: las :e7- fiV.v e?iablL?h€vl by the observations which 
ij.Tf :•{* r. milr cn^ler the direction of the Smithsonian 
I-r?r::c:::ii. and fnr^m other sources of information, that the 
: r:.v::j5a! disturbances of the atmosphere are not of a local 
: ♦. -racter. but commence in certain regions, and are propa- 
ca:^:-.! in definite directions over the whole surface of the 
United States east of the Rocky Mountains. 

From a careful study of all the phenomena of the winds 
of the temperate zones it is infernxl that over the w^hole sur- 
face of the United States and Canada there are two great 
currents of air continually flowing eastward. These cur- 
Tvnts oMisist of an upper and a lower, the former returning 
:he air to the south which was carried by the latter towards 
iho north. The lower current, which is continually flowing 
over the surface of the Uniteil States, is about two miles in 
depth, and moves from the southwest to northeast. The 
upjx^r or return current, which is probably of nearly equal 
ma*^niiude, flows from northwest to southeast, or nearly at 
rv^ht anirlcs to the other, and the resultant of the two is a 
current almost directly from the west. The reaction of these 
two currents apiH\nrs to be the principal cause of the sudden 
changesof weatlier in our latitude. They give definite direc- 
tion to our storms, accordingly as the latter arc more rnflu- 
enceil by the motion of the one or the other of these great 
aerial streams. The principal American storms may from 
our present knowledge, be divided into two classes, namely 
tboee which have their origin in the Caribbean Sea and 



1859] WRITINGS OF JOSEPH HENRY. 439 

tliose which enter our territory from the north at the eastern 
base of the iJocky Mountains. Those of the first class, which 
have been studied with much success by the lamented Red- 
field and others, follow the general direction of the Gulf 
Stream, and overlapping the eastern portion of the United 
States, give rise to those violent commotions of the atmos- 
phere which are in many instances so destructive to life and 
property along our eastern coast. These storms from the 
south are frequently two or three days in traversing the dis- 
tance from Key West to Cape Race, and their approach and 
progress might generally be announced by telegraph in time 
to guard against their disastrous effects. Though the gen- 
eral direction of these storms appears to be made out with 
considerable certainty, much remains to be done in settling 
the theory of their character and formation. 

The materials which have been collected at the Smithson- 
jan Institution during the last seven years relative to the 
other class of storms have enabled us to establish general 
facts of much value, not only in a scientific point of view, 
but also in their application to the prediction of the weather. 
[This statement was verified by a series of maps, exhibited 
to the Academ}'^ by Professor Henry, on which were indi- 
cated the beginning and progress of some remarkable changes 
of weather.] From these maps it appears that the great 
disturbances of the atmosphere which spread over the sur- 
face of the United States enter our territory from the posses- 
sions of the Northwest or Hudson's Bay Compan}^ about 
the sources of the Saskatchewan, at the base of the Rocky 
Mountains, and are thence propagated south and east, until 
in many instances they spread over the whole of the United 
States and probably a large portion of the Britislv posses- 
sions. 

For example, the great depression of temperature which 
occurred in January of the present year, and which will be 
remembered by every one as the most marked cold period 
of the season, entered the territorv of the United States at 
the point before mentioned on the 5thl:)f January, and on 
the 6th reached Utah, on the 7th Santa Fe, and on the 8th the 



440 WRITINGS OF JOSEPH HENRY. [1859 

Gulf of Mexico, and passing onward it was felt in Guate- 
mala on the 10th. While it was advancing southward it 
was spreading over the continent to the east ; on the 7th it 
reached the Red River settlement and all places under the 
same meridian, down to the Gulf of Mexico. It reached the 
meridian of Chicago on the 8th, the western part of the State 
of New York on the 9th, New England on the 10th, and Cape 
Race on the 13th. It moved with about equal velocity over 
the Southern States and was observed at Bermuda on the 
12th. 

The remarkable frost of last June, so far as it has been 
traced, had the same origin and followed the same eastward 
course. The fact was also illustrated, (by the maps before 
mentioned,) that the warm periods which have occurred in 
past years have followed the same law of progression, and 
consequently their approach could have been announced to 
the inhabitants of the Eastern States several days in advance 
had a proper system of telegraphic despatches been estab- 
lished. 

The value of the telegraph in regard to meteorology has 
been full}' proved by the experience of the Smithsonian 
Institution. The Morser line of telegraph has kindly fur- 
nished the Institution during the last twelve months, free 
of cost, with a series of daily records of the weather from 
the principal stations over the whole country east of the 
Mississippi river and south of New York. In order to ex- 
hibit at one view the state of the weather over the portion of 
the United States just mentioned a large map is pasted on a 
wooden surface, into which, at each station of observation, a 
pin is inserted, to which a card can be temporarily attached. 
The observations arc made at about seven o'clock in the 
morning, and as soon as the results are received at the Insti- 
tution, an assistant attaches a card to each place from which 
intelligence has been obtained, indicating the kind of weather 
at the time; rain being indicated by a black card, cloudiness 
by a brown one, snow by a blue one, and clear sky by a 
white card. 

This meteorological map is an object of great interest to 



1859] WRITINGS OF JOSEPH HENRY. 441 

tho many persons from a distance who visit the Institution 
daily; all appear to be specially interested in knowing the 
condition of weather to wliich their friends at home are sub- 
jected at the time. But the value of the map is not confined 
to the gratification of this desire. It enables us to study 
the progress of storms, and to predict what changes in the 
weather may be expected at the east, from the indications 
furnished by places farther west. For example, if a black 
card is seen in the morning on the station at Cincinnati, in- 
dicating rain at that city, a rain storm may confidently be 
expected at Washington at about seven o'clock in the even- 
ing. Indeed, so uniformly has this prediction been verified, 
that last winter the advertising in the afternoon papers of the 
lectures to be delivered at the Institution that evening was 
governed by the condition of the weather in the morning at 
Cincinnati; a rainy morning at the latter inducing a post- 
ponement of the lecture. 

It must be evident, from the facts given, that if a system 
of telegraphing over the whole country east of the Rocky 
Mountains were established, information could bo given to 
the Middle and Eastern States of the approach of disturb- 
ances of the atmosphere, — of much value to the agriculturist, 
the ship-owner, and to all others who transact business af- 
fected by changes of weather, as well as of importance to 
tlie invalid and the traveller. Indeed, with a proper com- 
bination of the lines now in operation, daily intelligence 
might be obtained in the city of Boston whfch would be of 
the highest interest to its inhabitants. [Professor Henry 
mentioned Boston in particular, because this city is so situ- 
ated that the storms, both of the southern and western class, 
reach it after they have been felt in New York and in other 
places which are not so far cast and north.] It is necessary 
to remark that the same use of the telegraph is in a measure 
inapplicable to the inhabitants of Western Europe, since 
they live on the eastern side of an ocean, and cannot be ap- 
prised of the approach of storms from the west. For the same 
reason the general laws of storms are more conveniently 



442 WRITINGS OF JOSEPH HENRY. [1859 

studied by the meteorologists of this country than by those 
of Great Britain and France. 

It should be distinctly understood that the remarks which 
have been made in this communication relate to the more 
violent changes of the weather which occur in autumn, win- 
ter, and spring. The thunder showers which occur almost 
daily during the warm weather in summer have somewhat 
of a local character, and commence at the same time and 
frequently at the same hour for several days in succession, 
at the same and different places; but wherever they com- 
mence they move eastward over the country until they are 
exhausted. 

Professor Henry also spoke of the facts collected in regard 
to the nature of American storms, and their connection with 
the two great aerial currents continually flowing over the 
temperate zone. He considered that the great changes of 
the weather are principally due to the gradual production 
of an unstable equilibrium in the two currents by the accu- 
mulation of heat and moisture in the lower. 

He spoke in high terms of the importance of the labors 
of Mr. Espy in developing the theory of the upper motion 
of air and the evolution of latent heat in the production of 
storms. 

In reply to a question as to the possibility of crossing the 
Atlantic in a balloon, the Professor stated that he had little 
doubt, if the balloon could be made to retain the gas and to 
ascend into the upper current, it would be wafted across the 
ocean in the course of three or four davs. If it descended 
into the lower current it would be carried to the north of 
cast, and if it continued in tl\e upper current it would reach 
Europe south of the same point. The course could be 
changed, within certain limits, by ascending and descend- 
ing from one current to the other. The late balloon voyage 
from St. Louis to Jefferson county. New York, was of inter- 
est in confirming the theoretical direction of the great lower 
current of this latitude. 



1861] WRITINGS OP JOSEPH HENRY. 443 



ON THE UTILIZATION OF ATMOSPHERIC CURRENTS IN AERO- 
NAUTICS.* 

(From the Smithsonian Annual Report for 1860, pp. 118, 119.) 

March 11, 1861. 

Dear Sir: In reply to your letter of February 25, 1861, 
requesting that I would give you my views in regard to the 
currents of the atmosphere and the possibility of an applica- 
tion of a knowledge of them to aerial navigation, I present 
you with the following statement to be used as you may 
think fit. 

I have never had faith in any of the plans proposed for 
navigating the atmosphere by artificial propulsion, or for 
steering a balloon in a direction diSerent from that of the 
current in which the vehicle is floating. 

The resistance to a current of air offered by several thou- 
sand feet of surface is far too great to be overcome by any 
motive power at present known which can be applied by 
machinery of sufficient lightness. 

The only method of aerial navigation which in the present 
state of knowledge appears to afford any possibility of prac- 
tical application is that of sailing with the currents of the 
atmosphere. The question therefore occurs as to whether 
the aerial currents over the earth are of such a character that 
they can be rendered subservient to aerial locomotion. 

In ahswering this question I think I hazard little in 
asserting that the great currents of the atmosphere have 
been sufficiently studied to enable us to say with certainty 
that they follow definite courses, and that they may be ren- 
dered subservient to aerial navigation provided the balloon 
itself can be so improved as to render it a safe means of 
locomotion. 

It has been established by observations now extending 
over two hundred years, that at the surface of the earth 



* [A letter addressed to Mr. T. S. 0. Lowe, the Aeronaut, dated Wash- 
ington, D. C, March 11, 1861.] 



444 WRITINGS OF JOSEPH HENKY. [1861 

within the tropics, there is a belt along which the wind con- 
stantly blows from an easterly direction; and from the com- 
bined meteorological observations made in different parts of 
the world within the last few years, that north of this belt, 
between the latitudes of 30° and 60° around the whole 
earth, the resultant wind is from a westerly direction. 

The primary motive power which gives rise to these cur- 
rents is the constant heating of the air in the equatorial, 
and the cooling of it in and toward the polar regions ; the 
eastern and western deflections of these currents being due 
to the rotation of the earth on its axis. 

The easterly currents in the equatorial regions are always 
at the surface and have long been known as the trade winds, 
while the currents from the west are constantly flowing in the 
upper portion of the atmosphere, and only reach the sur- 
face of the earth at intervals, — generally after the occurrence 
of a storm. 

Although the wind (aithe surface) over the United States 
and around the whole earth between the same parallels, 
appears to be exceedingly fitful, yet when the average move- 
ment is accurately recorded for a numl^er of years, it is found 
that there remains a large resultant of a westerly current. 
This is well established by the fact that on an average of 
many years packet ships sailing between New York and 
Great Britain occupy nearly double the time in returning 
that they do in going. 

It has been full}^ established by contiimous observations 
for ten years collected at this Institution from every part of 
the United States, that as a general rule all the meteorologi- 
cal phenomena advance from west to east, and that the 
higher clouds always move eastwardly. We are therefore 
from abundant observations as well as from theoretical con- 
siderations, enabled to state with confidence that on a given 
day, whatever may be the direction of the wind at the sur- 
face of the earth, a balloon elevated sufficiently high would 
be carried eastwardly by the prevailing current in the upper 
or rather middle region of the atmosphere. 

I do not hesitate therefore to say that provided a bal- 



1861J WRITINGS OF JOSEPH HENRY. 445 

loon can be constructed of sufficient size and of sufficient 
impermeability to gas to maintain a high elevation for 
a sufficient length of time, it would be wafted across the 
Atlantic. I would not however advise that the experi- 
ment of this character be made across, the ocean, but that 
the feasibility of the project should be thoroughly tested 
and experience accumulated by voyages over the interior 
of our continent. It is true that more eclat might bo 
given to the enterprise and more interest excited in the 
public mind generally by the immediate attempt of a pas- 
sage to Europe; but I do not think the sober sense of the 
more intelligent part of the community would be in favor 
of this plan; on the contrary, it would be considered a pre- 
mature and fool-hardy risk of life. 

It is not in human sagacity to foresee prior to experience 
what simple occurrence, or what neglect in an arrangement, 
may interfere with the result of an experiment; and there- 
fore I think it will be impossible for you to secure the full 
confidence of those who are best able to render you assist- 
ance, except by a practical demonstration in the form of 
successful voyages from some of the interior cities of the 
continent to the seaboard. 



446 WRITINGS OF JOS£PU HEN&Y. [1865 



SYSTEMATIC METEOROLOGY IN THE UNITED STATES. 
(From the Smithsonian Annual Report for 1865, pp. 50-59.) 

It has been aptly said that man is a meteorologist by 
nature. He is placed in such a state of dependence upon 
the atmospheric elements, that* to watch their vicissitudes 
and to endeavor to anticipate their changes become objects of 
paramount importance. Indeed the interest in this subject 
is so absolute that the common salutation among civilized 
nations is a meteorological wish, and the first introduction to 
conversation among stangers is a meteorological remark. Yet 
there is no circumstitnce which is remembered with so little 
exactness as the previous condition of the weather, even from 
week to week. In order that its fluctuations may be preserved 
as facts of experience, it is necessary that they should be con- 
tinuously and accurately registered. Again, there is perhaps 
no branch of science relative to which so many observations 
have been made and so many records accumulated, and yet 
from which so few general principles have been deduced. 
This has arisen, first, from the real complexity of the phe- 
nomena, or in other words from the number of separate 
causes influencing the production of the ordinary results; 
second, from the improper methods which have been pur- 
sued in the investigation of the subject, and the amount of 
labor required in the reduction and discussion of the obser- 
vations. Although the primary causes of the change of the 
weather arc on the one hand, the alternating inclination of 
the surface of the earth to the rays of the sun, by which its 
different parts are unequally heated in summer and in 
winter, and on the other, the moisture which is elevated 
from the ocean in the warmer and precipitated upon the 
colder portions of the globe ; yet the effects of these are so 
modified by the revolution of the earth on its axis, the con- 
dition and character of the different portions of its surface, 
and the topography of each country, that to strictly calcu- 
late the perturbations or predict the results of the simple 
laws of atmospheric equilibrium with that precision which 



1865] WRITINGS OF JOSEPH HENRY. 447 

is attainable in astronomy, will probably ever transcend the 
sagacity of the wisest, even when assisted by the highest 
mathematical analysis. But although such precision cannot 
be looked for, approximations may still be obtained of great 
importance in their practical bearing on the every-day busi- 
ness of life. 

The greater part of all the observations which have been ' 
recorded until within a few years past has been without 
system or co-ordination. It is true that the peculiar climate 
of a given place may be determined by a long series of 
isolated observations, but such observations, however long 
continued, or industriously and accurately made, can give 
no adequate idea of the climate of a wide region, of the 
progress of atmospheric changes, nor can ' they furnish an 
approximation to the general laws of the recurrence of phe- 
nomena. For this purpose a system of observation must 
be established over widely extended regions within which 
simultaneous records are made and periodically transmitted 
to a central position, where by proper reduction and discus- 
sion, such general conclusions may be reached as the mate- 
rials are capable of yielding. 

In discussing the records, the empirical method does not 
suffice. It is necessary that a priori assumptions should be 
provisionally adopted, not however at random, but chosen 
in strict accordance with well-established physical principles, 
and that these bo finally adopted, rejected, or modified, as 
they are found to agree or disagree with the records. It is 
only by this method that thc'different causes which co-operate 
in the production of a series of complex phenomena can bo 
discovered, as is illustrated in the history of astronomy, 
which previous to the investigations of Kepler consisted of 
an unintelligible mass of records of observations. But even 
with the application of the best possible process of discussion 
the labor necessary to be expended on such large masses of 
figures, in order to deduce simple results, is far beyond any 
individual efibrt, and can only be properly accomplished by 
governmental aid. 
The importance of a combined system of meteorological 



448 WRITINGS OF JOSEPH HENRY. [1865 

observations extending over a large area, and the peculiar 
advantages presented by our country for this object, were 
early appreciated, and such a system was commenced in 
]819, under the direction of Dr. Lovell, Surgeon General of 
the Army. The stations embraced the principal military 
posts, from which reports were made at the end of each 
month as to the temperature, the pressure, and the moisture 
of the air, the amount of rain, the direction and force of 
the wind, the appearance of the sky, besides casual phe- 
nomena, such as the aurora, thunder-storms, shooting stars, 
&c. In 1825 a similar system, of more numerous stations 
in proportion to the area embraced, was established in the 
State of New York, the points of observation being the 
several academies under the direction of the board of regents 
of the University, an establishment having charge of the 
higher institutions of learning in that State. 

In 1837 the Legislature of Pennsylvania made an appro- 
priation of four thousand dollars for instruments, which were 
distributed to volunteer observers. This system was con- 
tinued about ten years ; that of New York has been kept up 
with more or less efficiency until the present time ; while 
the army system was continued until the commencement of 
the war. 

The lake system, established by the engineer department, 
under the superintendence of Captain (now General) Meade, 
consists of a line of stations, extending from the western part 
of Lake Superior to the eastern part of Lake Ontario, and 
has been efficiently continued for several years. 

The Smithsonian meteoroloojical system was commenced 
in 1849, and with occasional aid in defraying the expenses, 
has continued in operation until the present period. It 
was however much diminished in efficiency during the war, 
since from the southern States no records were received, and 
many of the observers at the north were called to abandon 
such pursuits for military service in the field. The eflForts 
of the Institution in this line have been directed to supple- 
menting and harmonizing all the other systems, preparing 
and distributing blank forms and instructions, calculating 



1865] WRITINGS OF JOSEPH HENRY. 449 

and publishing extensive tables for the reduction of obser- 
vations, introducing standard instruments, and collecting 
all public documents, printed matter, and manuscript records, 
bearing on the meteorology of the American continent, sub- 
mitting these materials to scientific discussion, and publish- 
ing the results. In these labors the Institution has been in 
continued harmonious co-operation with all the other eflforts 
made in this country to advance meteorology, except those 
formerly conducted by the Navy Department under Lieuten- 
ant Maury. These were confined exclusively to the sea, and 
had no reference to those made at the same time on land. 
Without desiring to disparage the labors of Lieutenant 
Maury, I may say that his results would have lost nothing 
of their value by the adoption of a less exclusive policy on 
his part. The meteorology of the sea and that of the land 
pertain to a connected series of phenomena which can be 
properly studied only by a combined system of observations 
relating to both. The method pursued by Lieutenant Maury 
consisted in dividing the surface of a map of the ocean into 
squares of ten degrees on a side, and in recording within 
each of these the direction of the winds obtained from the 
log-books of the vessels which had traversed the several 
regions. In this way he accumulated a large amount of 
data, which though published in connection with many 
crude hypotheses, are of great vahie in the study of the 
meteorology of the globe. 

In 1853 a meteorological system was commenced in Can- 
ada, the senior grammar school in each county being pro- 
vided with instruments ; and the observations have been 
continued to the present time. In regard to this system, 
Mr. Hodgins of the educational department remarks: "We 
have never lost sight of the great practical importance to a 
new and partially settled country, of establishing early in 
its history, before its physical condition is materially changed, 
a complete and comprehensive system of meteorological 
observations, by which may be tested theories of science 
which are yet unsettled, and which may be solved, relating 
to natural phenomena which have long remained among 
the sealed mysteries of nature." 

20-2 



450 WRITINGS OF JOSEPH HENRY. [1865 

The observations thus far have been taken without remun- 
eration, but the importance of the system has become so well 
recognized, that the Canadian government has decided to 
establish ten permanent stations, in addition to the observa- 
tories at Toronto and Kingston, distributed so as to afford 
the most complete information relative to the climatic fea- 
tures of the whole province. The points selected are Wind- 
sor, Goderich, Stratford, Simcoe, Barrie, Hamilton, Peter- 
borough, Belleville, Pembroke, and Cornwall ; that is, two 
stations on Lake Erie, one on Lake Huron, three on Lake 
Ontario, one on Lake Simcoe, one on the Ottawa river, one 
on the bay of Quinte, one on the St. Lawrence, near the 
eastern extremity of the province, and two in the interior of 
the country. The records made at the public schools of 
Canada have been furnished to the Smithsonian Institution, 
as well as to the committee on immigration of the New York 
House of Assembly, for the purpose of furnishing facts rela- 
tive to the climate — of importance to settlers ; and recently 
the department of royal engineers has applied for the re- 
turns, with a view to the consideration of their bearing on 
questions of defence. To secure a greater degree of respon- 
sibility, and to promote the efficiency of the system, the gov- 
ernment has provided for the payment of fifty cents a day 
to the teachers of the grammar schools at the stations before 
enumerated, as remuneration for the service rendered. 

Under the direction of the distinguished academician Kup- 
fer, there is established oyer the vast Russian territory a 
network of thirty meteorological stations, where are noted 
the various changes of the atmosphere as to temperature, 
pressure, moisture, &c. The most northern of these stations 
is at Hammerfest, in 70° 41' north latitude, 21° 2G' cast 
longitude from Paris, and the most southern is at Tiflis, in 
41° 42' north latitude, and 42° 30' east longitude. 

A like svstem of simultaneous observations has been* for 
several years in operation in Great Britain and Ireland, in 
conniption with the Board of Trade, and under the direction 
of the late Admiml Fitzroy. 

Other and similar systems of meteorology have been 



1865] WRITINGS OF JOSEPH HENHY. 451 

established in France, Italy, and Holland. From these dif- 
ferent organizations, as well as from insulated observatories, 
telegrams of the weather are sent every morning, at seven 
o'clock, from the principal cities of Europe to Paris, where 
under the superintendence of the celebrated Leverrier, they 
are discussed, and the results transmitted by' mail to all 
parts of the world in the successive numbers of the daily 
International Bulletin. A similar publication is periodi- 
cally made in Italy, under the direction of M. Matteucci, so 
well and favorably known by his discoveries in physics. 
The British Government has also established a system of 
observations for the sea, and furnished its navv with accu- 
rate instruments, carefully compared with the standards of 
the Kew observatory. It is estimated in a report to Parlia- 
ment that through an annual appropriation of about fifty 
thousand dollars, statistics may be collected in fifteen years 
sufiicient, with what has already been obtained, to deter- 
mine the average movement of the winds on every part of 
the ocean. 

From the great interest which has been awakened in 
regard to meteorology throughout the world, and the 
improved methods which have been adopted in its study, it 
can scarcely be doubted that in a few years the laws of the 
general movements of the atmosphere will be ascertained, 
and the causes of many phenomena of tlie weather, which 
have heretofore been regarded as little else than the capri- 
cious and abnormal impulses of nature, will become ade- 
quately known; although, from the number of these causes', 
and the complexity of the resultant effect, it may never be 
possible to deduce accurate predictions as to the time and 
l)articular mode of their occurrence. 

Indeed, the results which have been already derived from 
the series of combined observations in this country, fully 
justify the wisdom and forethought of those who were instru- 
mental in establishing them. Although their organization 
was imperfect, the observers in most cases untrained, and 
the instruments of an inferior character, yet they have fur- 
nished data which through the labors of Redfield, Espy, and 



452 WHITINGS OP JOSEPH HENRY. [1865 

Hare, whose memories are preserved in the history of science, 
have led to the establishment of principles of high theoreti- 
cal interest, as well as of great practical value. Among these 
I need here mention only the fact now fully proved that all 
the meterological phenomena of at least the middle and 
more northern portions of the temperate zone are trans- 
mitted from west to east. The passage of storms from one 
part of the country to the other was noticed by Dr. Franklin 
on the occasion of observing an eclipse of the moon. He 
showed that our south-west storms are felt successivelv later 
and later as the point of observation is farther to the north- 
east; that they arrive last at the extreme north-eastern por- 
tions of our continent. We now know however that the sue- 
cessive appearance of the storm at points farther along the 
coast is due to the easterly movement — sideways as it were, 
of an atmospheric disturbance, greatly elongated north and 
south, and reaching sometimes from Canada to the Gulf of 
Mexico. Hence to persons residing along the seaboard the 
phenomenon would appear to have a northwardly progres- 
sion, on account of the north-easterly trend of the coast ; yet 
the storm not unfrequcntly reaches simultaneously Bermuda 
and Nova Scotia. 

Few persons can have failed to observe the continued 
motion of the higher clouds from the west, or to have recog- 
nized the just metcoroscopy of Shakspeare in a well-known 
passage : 

** The wcury sun hath made a golden set, 
And hy the bright track of his fiery car 
Gives token of a goodly day to-niorrow." 

The breaking forth of the sun just before his setting shows 
that the rear of the cloud which has obscured his beams 
has in its easterly course reached our horizon, and will soon 
give place to an unobscured sky. 

It must be observed however that all the storms which 
visit our coast are not of this nature; those denominated 
cyclones, and which seldom extend far into the interior, are 
probably of a rotatory character. These usually commence 
in the Caribbean sea, move first toward the northwest, and 



1865] WHITINGS OF JOSEPH HENRY. 453 

gradually curving round before they reach our latitude, take 
an easterly direction, as has been shown by Redfield and 
others. 

The first practical application which was attempted of the 
principle we have mentioned was made by this Institution 
in 1856; the information conveyed by telegraphic despatches 
in regard to the weather was daily exhibited by means of 
differently colored tokens, on a map of the United States, so 
as to show at one view the meteorological condition of the 
atmosphere over the whole country. At the same time pub- 
lication of telegraphic despatches was made in the newspa- 
pers. The system however was necessarily discontinued at 
the beginning of the war, and has not yet been resumed. 
Similar applications have since been made in other coun- 
tries, particularly in England, under the late Amiral Fitz- 
roy; in France, under Leverrier; and still later, in Italy. 
In the last-mentioned country tabular statements are to bo 
published annually, comparing the predictions with the 
weather actually experienced. 

The British Government has also recently introduced the 
system of telegraphic meteorological predictions into India. 
The cyclone of October, 1864, which did such damage to the 
shipping in Calcutta and destroyed the lives of sixty thou- 
sand persons, called special attention to the subject. The 
Asiatic Society of Bengal estimated the cost of such a system 
at 67,000 rupees (about $30,000), a sum which the govern- 
ment hesitated to appropriate, though it decided to furnish 
the necessary instruments and an allowance of fifty rupees 
a uionth to the assistant at the telegraph station at Sau- 
gor, on the seaboard to the southward of Calcutta, in the 
direction from which the most severe storms approach that 
port. 

It must be evident from what we have said in regard to 
the movement of storms, that a system of telegraphic meteo- 
rological predictions would be at once more reliable and of 
more benefit to the eastern coast of the United States, than 
those made in England and France, on the western coast of 
Europe, could possibly be to those countries, since the dis- 



454 WRITINGS OF JOSEPH HENRY. [1865 

turbances of the atmosphere which reach them advance from 
the ocean, while the majority of those of a similar nature 
which visit especially the middle and eastern portions of our 
coast, come overland from a westerly or south-westerly direc- 
tion, and their approach may be telegraphed in some cases 
many hours before their actual arrival. 

But the expense of the proper establishment of a system 
of this kind can only be defrayed by the general government 
or some organization in possessio'n of more ample means 
than can be applied by the Smithsonian Institution to such 
a purpose. This will be evident from the fact which we 
have mentioned of the cost of the establishment of a similar 
system in India, and from a report of a committee of the two 
houses of Parliament appointed to consider certain questions 
relating to the meteorological department of the board of 
trade. From this it appears that the amount expended 
during the eleven years ending with 1865 was 45,000 pounds 
sterling, or an average of about $20,000 a year. The same 
committee recommend that meteorological observations at sea 
be continued under the direction of the hydrographic office of 
the admiralty, and an appropriation of £1,500 annually be 
made for instruments, and £1 ,700 for discussion and publica- 
tion of results ; making a total of £3,200. For weather statis- 
tics on land, the annual sum of £4,250, including instruments, 
discussion, and publications, is recommended, and for tele- 
gram storm warnings, £3,000; making a total annual ex- 
penditure of £7,450 for the land, and a grand annual total 
for land and sea of £10,450, or $52,250. 

The present would appear to be a favorable time to urge 
upon Congress the importance of making provision for 
re-organizing all the meteorological observations of the 
United States under one combined plan, in which the rec- 
ords should be sent to a central depot for discussion and 
final publication. An appropriation of $50,000 annually for 
this purpose would tend not only to advance the material 
interests of the country but also to increase its scientific reputa- 
tion. It would show that although the administration of our 
Government is the expression of the popular will, it is not 



1865] WRITINGS OF JOSEPH HENRY. 455 

limited in its operation merely to objects of instant or imme- 
diate utility, but that with a wise prevision of the future it 
withholds its assistance from no enterprise, however remote 
the results, w^hich has for its end to advance the well-being 
of humanitv. 

It is scarcely necessary at this day to dwell on the advan- 
tages which result from such systems of combined observa- 
tions as those which the principal governments of Europe 
have established and are now constantly extending. I may 
however in passing, briefly allude to some facts which may 
not at once occur to the mind of the general reader. They 
enable the mariner to shorten the time and diminish the 
danger of the passage from one port to another by indicating 
to him the route along which prevail at a particular season 
of the year the most favorable winds for his purpose. They 
also furnish the means by which the sailor is taught the 
important lesson which has saved thousands of lives and 
millions of property, namely, that of finding the direction 
of the centre of the cyclone, and of determining the course 
in which he must steer in order to extricate himself from 
the destructive violence of this fearful scourge of the ocean. 
To the agriculturist they indicMe the character of the climate 
of the country, and enable him with certainty to select the 
articles of culture best adapted to the temperature and mois- 
ture of the region, and which in the course of a number of 
years will insure him the most profitable returns for his 
labor. They furnish the statistics of the occurrence of sterile 
years and of devastating storms, w^hich may serve as the 
basis on which to found insurance institutions for protection 
against the failure of crops, and thus give to the husband- 
man the same certainty in his pursuits as that possessed by 
the merchant or the ship-owner. They may also afford 
warning of the approach of severe frosts and violent storms, 
in time to guard at least in some degree against their inju- 
rious effects. To the physician a knowledge of such results 
as can be obtained from an extended system of observations 
is of great importance, not only in regard to the immediate 
practice of his art, but also to the improvement of his science. 



45G WUITIXGS OF JOSEPH HENRY. [1865 

The peculiar diseases of a region are principally dependent 
on its climate; an extreme variation of temperature in a 
large city is invariably attended with an increase of the 
number of deaths. The degree and variation of the mois- 
ture at different times and in different places have also a 
great influence on diseases, and the more the means of study- 
ing the connection of these elements and the corresponding 
condition of the human body are multiplied the more will 
the art and the science of medicine be improved. I may 
mention that scarcely a week passes at the Institution in 
which application is not made for met^jorological informa- 
tion relative to different parts of this country, with the hope 
to improve the condition, if not restore the health, of some 
patient. The knowledge which at present exists however 
as to the connection of climate and disease, particularly in 
our own country, is — in comparison to what might be ob- 
tained — of little significance. 

No other part of the world can at all compare with this 
country in the conditions most favorable to the advancement 
of meteorology, by means of a well-organized and properly 
sustained system of combined observations. Such a system 
extending from cast to west more than two thousand miles 
would embrace in its investigation all the phenomena of the 
great upper current of the return trade wind, which con- 
tinually flowing over us at a hi^h elevation carries most of 
the disturbances of the atmosphere eastward. It would also 
include the effects produced by the polar and equatorial 
currents as they contend for the mastery along the broad 
valley which stretches without interruption from the arctic 
circle to the Gulf of Mexico, and would settle with precision 
the influence of the great fresh-water lakes in ameliorating 
the climate of the adjacent regions. But above all, in a 
popular view, it would furnish the means more effectually 
than any other system — of predicting the approach of storms 
and of giving the ships of our Atlantic coast due warning 
of the probability of danger. 



1866] WRITINGS OP JOSEPH HENRY. 457 



REMARKS ON "VITALITY."* 
(From the Smithsonian Annual Report for 18G6, pp. 38G-388.) 

In the early study of mechanical and physiological phe- 
nomena, the energy which was exhibited by animals, or in 
other words, their power to perform what is technically 
called work, that is to overcome the inertia and change the 
form of matter, was referred to the vital force. A more criti- 
cal study of these phenomena has however shown that this 
energy results from the mechanical power stored away in 
the food and material which the body consumes ; that the 
body is a machine for applying and modifying power, pre- 
cisely similar to those machines invented by man for a 
similar purpose. Indeed, it has been shown by accurate 
experiments that the amount of energy developed in animal 
exertion is just in proportion to the material consumed. To 
give a more definite idea of this, we may state the general 
fact that matter may be considered under two aspects, namely 
matter in a condition of power, and matter in a state of entire 
inertness. For example, the weight of a clock or the spring 
of a watch when wound up is in a state of power, and in its 
running down gives out, tick by tick, an amount of power 
precisely equal to the muscular energy expended in winding 
it up. When the weight or the spring has run down, it is 
then in a condition of inertness, and will continue in this 
state, incapable of producing motion, unless it be again 
put in a condition of power by the application of an extrane- 
ous force. Again, coal and other combustible bodies consist 
of matter in a condition of power, and in their running down 
into carbonic acid and water, during their combustion, evolve 
the energy exhibited in the operations of the steam engine. 
The combustible material may be considered the food of the 
steam engine, and experiments have been made to ascertain 

♦[Remarks on a communication **0n Vitality," by the Rev. H. H. Hig- 
gins, in the Proceedings of the Literary and Philosophical Society of Liver- 
pool, (England,) 1864. Re-printed in the Smithsonian Report for 186G, pp. 
879-886.1 



45S WRITINGS OF JOSEPH HEXRT. [1866 

the relative economy in the expenditure of a definite amount 
of foo<J in the natural machine and the artificial engine. 
The former has been found to waste less of the motive power 
than the latter. 

In pursuing this train of investigation the question is 
asked, " Whence does the coal or food derive its power?" 
The answer is, that these substances are derived from the 
air by the decomjiosing agency of the impulses from the sun, 
and that when burned in the engine or consumed in the 
boily they are again resolved into air, giving out in this 
resolution an amount of energj' equivalent to that received 
from tlie sun during the process of their growth. All the 
materials of the crust of the earth, with the exception of coal 
and organic matter, are in a state of inertness, and like die 
burnt slag of the furnace, have expended their energy, and 
in tills condition of inertness they would forever remain, 
were it not for extraneous influences, principally that from 
the sun. 

From this point of view the phenomena we have been 
considering consist merely in the transfer of power from one 
l)ody to another, and from a wide generalization from all 
the facts, the conclusion has been arrived at that energy is 
neither lost nor gained in the transfer; and pursuing the 
same train of reflection, we are finally led to the result that 
all power is derived from the primordial, unbalanced attrac- 
tion and repulsion of the atoms of matter. 

In the gradual development of the principles we have 
given there has been a tendency to extend the views we 
have presented too far, and to refer all the phenomena of life 
to the mechanical or chemical forces of nature. Although 
it has been, as we think, conclusively proved that from food, 
and food alone, come all the dittcrent kinds of physical force 
which are manifest in animal life, yet as the author of the 
l)reccding paper has shown, there is something else neces- 
sary to life, and this something, though it cannot properly 
be called a force, may be denominated the vital principle. 
Without the influence of this principle the undirected physi- 
cal powers produce mechanical arrangements and assume a 



1866] WRITINGS OF JOSEPH HENRY. 459 

state of permanent equilibrium by bringing matter into 
crystalline forms or into a condition of simple aggregation, 
while under its mysterious influence the particles of matter 
are built up into an unstable condition in the form of or- 
ganic molecules. While therefore we may refer the changes 
which are here produced, or in other words the work per- 
formed, to the expenditure of the physical powers of heat, 
chemical action, &c., we must admit the necessity of some- 
thing beyond these which from the analogy with mental 
phenomena, we may denominate the directing principle. 
Although we cannot perhaps positively say in the present 
state of science that this directing principle will not manifest 
itself when all the necessary conditions are. present, yet in 
the ordinary phenomena of life which are everywhere 
exhibited around us, organization is derived from vitality, 
and not vitality from organization. That the vital or direct- 
ing principle is not a physical power which performs work, 
or that it cannot be classed with heat or chemical action, is 
evident from the fact that it may be indefinitely extended 
— from a single acorn a whole forest of oaks may result. 

The principles of which we have here endeavored to give 
an exposition are strikingly illustrated in the transformation 
of the egg when subjected to a slightly elevated temperature. 
The egg of a bird for example consists, as we know, of a 
congeries of organized molecules or vesicles, enclosed in a 
calcareous shell, thickly punctured with minute holes, through 
which the oxygen of the air can enter, and vapors and gases 
escape. Let us observe the difference of changes which take 
place in two newly-laid eggs, one of which is not possessed 
with vitality, and the other is endowed with this mysterious 
principle. Both of these eggs are in a condition of power, 
the carbon, hydrogen, nitrogen, sulphur, &c., of which their 
organized molecules are composed, are in a state of unstable 
equilibrium and ready, when set in motion by a slight in- 
crease of temperature, to rush into the more stable compounds 
of carbonic acid, vapor of water, (fcc, by chemical attraction. 
While the eggs are in an unchanged condition they possess 
the same amount of what is called potential energy, which 



4G0 WRITINGS OF JOSEPH HENKY. [1866 

in both cases will be expended in the transformation of the 
materials; but how different will bo the effects produced. 
In the case* of the egg deprived of vitality, all the organized 
molecules will be converted into gases and vapors, with the 
development of heat and an elastic energj% in some cases 
sufficient to burst the shell, the power originally stored away 
in the egg being thus dissipated in the production of chemi- 
cal and mechanical changes. In the case of the egg pos- 
sessed of vitality, a portion of the organized molecules will 
also run down into vapors and gases, which will gradually 
escape through the perforations of the shell, and will thus, 
as in the previous case, evolve an equivalent amount of 
power; but this, instead of being dissipated in mere mechani- 
cal or chemical effects, will be expended, under the directing 
principle of vitality, in elevating to a higher degree of organ- 
iziition the molecules of the remainder, and in transforming 
tliem into organs of sensation, perception, and locomotion ; 
in short, in the production of a machine precisely similar to 
those constructed by the intellectual operations of man when 
guiding or directing the powers of nature. If w^e examine 
the transformation as it goes on from day to day, we shall 
see that it does not consist in a simple aggregation of parti- 
cles in the production of the organs we have mentioned, but 
in preliminary arrangements, such as canals, and provis- 
ional parts, afterwards to be obliterated, and the adoption of 
means for a more remote end, the whole indicating an in- 
tention realized in the sentient, living, moving animal. 

This vital principle, from strict analogy, cannot be consid- 
ered as an essential proi)erty of matter, since it is only contin- 
ued by transmission from one living being to another. It is 
true that it ceases to. manifest itself when a slight derange- 
ment takes place in the organized material with which it is 
connected, and death ensues; but this is precisely analogous 
to the manifestation of the thinking, willing principle within 
us, the existence of which is revealed to us by our own con- 
sciousness as a primordial truth, beyond which nothing can 
be more certain. 



1870] WRITINGS OF JOSEPH HENRY. 461 



SUGGESTIONS AS TO THE ESTABLISHMENT OF A PHYSICAL 

OBSERVATORY.* 

(From the Smithsonian Annual Report for 1870, pp. 141-144.) 

December 29, 1870. 

My Dear Sir: Yours of the 28th of November was duly 
received, but I delayed answering it until the pressure of 
business which accumulated during my absence should have 
somewhat subsided, and also that I might receive the plans 
which you mention. I am now gratified in being able to 
inform you that my visit to Europe was both pleasant and 
profitable, and that I have returned much inproved in health, 
and with enlarged views as to the present state of science in 
the Old World. 

While abroad I gave special attention to physical obser- 
vatories, of which there are several in England and on the 
continent, although no one of them fully realizes my idea 
of what such an establishment ought to be. 

A physical observatory is one the primary object of which 
is to investigate the physical phenomena of the earth and the 
heavenly bodies in contradistinction to an ordinary astronom- 
ical observatory, which is principally devoted to the observa- 
tion and discussion of the motions of the planets, and the deter- 
mination of the relative positions of the fixed stars. Of the 
latter kind but one or two are needed in any country, and as 
these require a numerous corps of observers and computers 
they can only be supported by appropriations annually from 
a national government. Tlie United States Observatory at 
Washington is of this character, and including all expenses 
requires an annual appropriation of at least $50,000. The 
labors of such an observatory are indispensible to the advance- 
ment of the science of theoretical astronomy, and its appli- 
cation to geodesy and geography. 

The establishment I would advise you to found is of the 
character of the one first mentioned, namely a physical ob- 
servatory, the principal object of which would be, as I have 

*[A letter addressed to Mr. Lcander McCormick, dated Washington, 
December 29, 1870.] 



102 WRITINGS OF JOS£l*U HENRY. [1870 

indicaicd, to investigate the nature and changes of the con- 
stitution of the heavenly bodies ; to study the various ema- 
nations from tliese in comparison with the results of ex|)eri- 
ments, and to record and investigate the different phenomena 
which are included under the general term of terrestrial 
physics. 

A wide field has been opened for the study of the nature 
of the sun and other heavenly bodies by the application of 
the spectroscope, diflFerent modifications of the telescope, and 
other lately invented appliances. We now know that the 
sun is undergoing remarkable changes, the character of 
which can only be ascertained by the results of accurate 
observations compared with those of experimental investi- 
gation. The observer should divide his attention between 
the phenomena revealed by a critical and continued exami- 
nation of the sun and the production of similar phenomena 
in the lalH)ratory. In this way European investigators have 
arriveii at most interesting results. 

Again, we know that the emanations from the sun, and 
probably from the stars, differ essentially in character. 
There is first, the emanation known as light, which of itself 
consi^b^ o( various rays (generally indicating the incau- 
des4.vnoo of ?ubstanct»s.) that give the sensation of different 
colore, sonic of which though in their ordinary condition 
iin|x^rvvpiil>le to the eye, may be perceived by that organ 
after they have passed through certain liquids; next, the 
heat emanation, which is also of different kinds; then 
tlie ehoniieal emanation, by which photographic im- 
pressions an.» proiluced ; and lastly, the phosphorogenic 
emanation (abounding also in the electric discharge), that 
pnxluces the temiKirary glow of the diamond and the 
luminosity of the compounds of lime, barium, and other 
substances with sulphur, when taken into the dark. To 
study these or other emanations as they may appear 
in the tixed stars, or are reflecteil from the moon and 
planets, or iis they may be found in the aurora borealis, the 
zodiacal light, and in shooting-stars or larger meteors, re- 
quires i>eculiar instruments, and such as are not found, at 



1870] WRITINGS OF JOSEPH HENRY. 463 

present, in ordinary astronomical observatories. For ex- 
ample, the celestial plienomena which address themselves to 
the sense of sight are studied by means of refracting tele- 
scopes, as are also those of the photographic ray, although 
this requires a peculiar form of lens, while the heat-ray of 
lower intensity and the pliosphorogenic ray are not trans- 
mitted by glass; the former is readily converged to a focus 
by a lens of rock-salt, and the latter by one of quartz. They 
may all however as in the case of light, be concentrated into 
foci by metallic reflectors. 

In regard to terrestrial physics, the phenomena are also 
various, and the forces by which they are produced are con- 
stantly changing both in intensity and in some cases in 
direction. We now know that the magnetism of the earth 
scarcely remains the same from one moment to another, and 
that tliese changes are connected with the appearance of the 
aurora borealis and electrical discharges in the atmosphere. 
They also in all probability may ultimately be referred to 
disturbances produced by external influences, such as those 
from the sun, moon, and planets. Furthermore, we may 
now consider the whole earth as an immense conductor 
charged with negative electricity, of which the intensity is 
in a continued state of change, and of the laws of which, 
as well as those of the changes of magnetism, a knowledge is 
highly desirable. For the proper study of these, continuous 
self-recording instruments are necessary. 

There is also an important field of observation in regard 
to ordinary meteorology, such as the changes of the pressure 
of the atmosphere, and its connection with other phenomena ; 
of the normal and abnormal winds; isolated currents of the 
atmosphere, and especially tliose of a vertical direction ; the 
radiation of heat from clouds and different terrestrial sur- 
faces ; the variation of its intensity in ascending above and 
penetrating below the surface of the earth, &c. In short, 
the field is almost boundless, and every year reveals new 
facts in terrestrial and celestial physics, which never fail to 
furnish new points for investigation to those who are quali- 
fied by education and endowed by nature for their proper 
appreciation. 



464 WRITINGS OP JOSEPH HENRY. [1870 

Tho conductor of an observatory such as I have mentioned 
to be successful must have peculiar characteristics. He must 
possess a minute knowledge of all the latest discoveries in 
physics, a keen ej'e to detect new appearances, imagination 
to suggest hypothetical causes, logical power to deduce con- 
sequences from these, to be tested by observation or experi- 
ment, and ingenuity to devise apparatus for verifying or 
disproving his deductions. When such a man is found he 
should be consecrated to science and fully furnished with 
all tho implements necessary for the prosecution of his 
researches, those of physics as well as of astronomy, and 
himself and family placed beyond all anxiety as to the 
supply of their necessary wants. It may not be amiss to 
combine with his studies and duties, in the way of research, 
a small amount of lecturing, — just enough by sympathetic 
communication with admiring pupils to fan as it were his 
enthusiasm, and to impart a portion of it to others. He 
should also have at his command a skillful workman who 
under his direction could construct the temporary apparatus 
which are constantly required in original research. It is 
also important tliat he be associated with the faculty of a well- 
endowed college or university, to which he will become an 
important acquisition both in regard to the reputation which 
ho will give to the institution and tho effect he will have on 
the other members of the faculty in the way of stimulating 
them to higher efforts. In such an association he can call 
for the co-operation of the professors, and especially that of 
the physicist, the chemist, and the mathematician. 

One of the most important points perhaps to which I 
should call your attention, is that of the building to bo 
erected, since from the tendency to error in this line more 
injury has resijted to public institutions in this country 
than from any other cause. It should be recollected that 
"money is power;" that every dollar possesses a definite 
amount of potential energy as it were which can always 
command intellectual or physical labor. But money as a 
power is unlike all other kinds of power in that it is by 
judicious investment capable of yielding a constant supply 



i 



1870] WRITINGS OP JOSEPH HENRY. 465 

of energy in the way of interest without diminishing the 
original amount. It is therefore in ilie highest degree in- 
judicious in the founding of an establishment to exhaust the 
source of its power by architectural displays not absolutely 
required and which may forever involve a continual expense 
from the remaining funds to keep them in repair. As a 
general rule the buildings of educational or scientific insti- 
tutions should be gradually evolved from the experience 
and wants of the establishment, and not as is too frequently 
the case from a priori misconceptions of those who have no 
adequate idea of the uses to which the structure is to bo 
applied. It should be impressed upon the public that buHd- 
ings do not constitute an institution, and that reputation and 
usefulness in science do not flow from visible and tangible 
manifestations, but are tlie immaterial fruit produced by 
the spirit of an organization. I trust that millions of human 
beings yet unborn will be familiar with the intellectual 
results of your observatory, although a single inquiry may 
never be made as to the style of the building in which these 
results have been produced. 

My advice then would be, first, if possible that the right 
man be procured for director; secondly, that the principal 
instruments be constructed under his supervision ; and 
thirdly, that the operations be commenced in an inexpen- 
sive wooden building, which will be found better in many 
respects for physical and astronomical observations than one 
of stone and brick. The instruments could be insured, I should 
think, at a small premium, and in that case if destroyed by 
fire might be replaced by others embracing the improve- 
ments which may have been suggested in the meantime. 

As an illustration of what I have just said in regard to 
the building, I may mention that on a visit to Mr. Lockyer 
I found him carrying on a series of observations which have 
challenged the admiration of the world in a temporary 
structure made of rough boards, unplastered, and scarcely 
including a space of fifteen feet square. 

As to the location of your observatory, you will infer from 
what I have said that I think it important to connect it with 
some well-endowed and well-established college or university. 

80-2 



466 WRITINGS OF JOSEPH HENRY. [1871 



EFFECT OF THE MOON ON THE WEATHER.* 
(From the Smithsonian Annual Report for 1871, pp. 460, 461.) 

Since the form of the orbit of the earth is aflfected by the 
attraction of Venus and the other planets, as well as by its 
satellite the moon, they must in some degree also affect the 
form of the atmospheric covering of the globe, and tend to 
produce tides which are of greatest magnitude when they are 
in opposition to or in conjunction with the sun. But whether 
these disturbances of the atmosphere or those produced by 
the moon are of such a character as to give rise to the violent 
atmospheric commotions denominated storms, is a question 
which has long agitated the scientific world. 

The times and peculiarities of the meteorological occur- 
rences are more varied and less definitely remembered than 
almost any other natural phenomena, and hence the large 
number of different rules for predicting the changes of the 
weather. The only way of accurately as(5ertaining the truth 
of any hypothesis in regard to atmospheric changes, is that 
of having recourse to trustworthy records of tlie weather 
through a long series of years, and it is one of our objects in 
collecting meteorological statistics at the Smithsonian Insti- 
tution to obtain the means of proving or dis-proving propo- 
sitions of the character you have advanced. 

The moon, being the body nearest to the earth, produces 
the highest tide in the waters of the ocean, and must also 
produce the greatest effect on the aerial covering of the earth. 
It has not been satisfactorily proved however that the occur- 
rence of the lunar tides is connected with appreciable changes 
in the barometrical or thermometrical condition of the at- 
mosphere. The less pressure of the air at a given place on 
account of the action of the moon, is just balanced by the 
increased height of tlie aerial column. 

The principal causes of the violent changes of the atmos- 

* [Letter to a correspondent in reply to inquiries and suggestions on the 
subject.] 



1871] WBITINGS OP JOSEPH HENRY. 467 

phero are due I think to its instability produced by the for- 
mation and condensation of vapor. It is not impossible that 
when the air is in a very unstable condition on account of 
the heat and moisture of the lower strata, the aerial tide may 
induce an overturning of the tottering equilibrium at some 
one place in the northern or southern hemisphere more un- 
stable than the others, and thus commence a storm which, 
but for this extraneous cause, would not have happened. 
To detect any such influence of the moon however, it will 
be necessary to compare simultaneously the records of the 
weather from day to day throughout all the northern and 
southern temperate zones, and to ascertain whether the 
maximum of these changes have any fixed relation in time 
to the changes of the moon. 

The changes of the moon take place at a given moment 
on every part of the earth; the greatest effect of a lunar tide 
ought therefore to bo felt in succession entirely around tho 
earth in the course of about twenty-four and one-half houre 

The problem cannot be determined however by such casual 
observations as those which you narrate. I have not the 
least idea that the attraction of Venus produces any appre- 
ciable effect. It is too small to produce a result which would 
be indicated by any of our meterological instruments. 

I am far from subscribing to the justice of your remarks 
in regard to Mr. Espy,^since I have a great respect for his 
scientific character, notwithstanding his aberration, in a 
practical point of view, as to tho economical production 
of rain. Tho fact has boon abundantly proved by observa- 
tion that a large fire sometimes produces an overturn in the 
unstable equilibrium of the atmosphere and gives rise to the 
beginning of a violent storm, but it was not wise in him to 
insist on the possibility of turning this principle to an eco- 
nomical use. 



468 WRITINGS OF JOSEPP HENKY. [1871 



ON THE ORGANIZATION OF A SCIENTIFIC SOCIETY.* 

(Bulletin of the Philosophical Society of Washington, vol. I, pp. v-xiv.) 

Ddh^ered November 18, 1871. 

Gentlemen: I have been requested to make some remarks 
on the character and object of this Society which may serve 
to introduce it to the world through the pages of a Bulletin 
of its proceedings, or the public journals of the day, and in 
compliance with tliis request, I beg leave to submit the fol- 
lowing reflections on the importance, as well as on the proper 
conduct of such an association. 

This Society was formed by the call for a meeting of a 
number of gentlemen impressed with the importance of an 
association of a strictly scientific character, in the city of 
Washington. At the meeting which resulted from this call, 
a name and a constitution were adopted for the Society, and 
without delay, in a series of subsequent meetings, the objects 
of the association were prosecuted with such marked success, 
as to fully